Your PC is dead silent. You press the power button, and nothing happens — no fans spin, no lights come on, no beep, no POST. Or maybe you get a half-second twitch of the fans before everything goes dark again. You might notice the LED on your motherboard is dark, or the PSU’s own fan never twitches. When a power supply fails to turn on, the entire system is starved of its primary input, so every other component appears dead too.
Here’s the good news: a PSU that won’t start is often not a dead PSU. A surprising number of these cases trace back to a tripped protection circuit, a loose AC cable, a switched-off power switch, or a stuck front-panel connector — all fixable in minutes. That said, this is also one of the few failures where the hardware itself can be genuinely dangerous, so before opening anything, unplug the system and give it several minutes for the capacitors inside the PSU to discharge. Never open the PSU case itself; internal capacitors hold lethal voltage long after unplugging. Work through the fixes below from easiest to hardest, and you’ll either have your machine back or know for certain it’s time for a replacement unit.
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Likely Causes
| Cause | How to confirm | Fix difficulty |
|---|---|---|
| Wall outlet, surge strip, or AC cable problem | Plug a lamp or phone charger into the same outlet; swap in a known-good AC cable | Very easy |
| PSU rear switch off or voltage selector wrong (115V/230V) | Look at the rocker switch and red slider on the PSU’s rear panel | Very easy |
| Tripped OCP/SCP/OVP protection latching the unit off | System twitched once, then stayed dead; happens after a short or new hardware install | Easy |
| Loose or incorrectly seated 24-pin or CPU power connector | Reseat both connectors; check the 4/8-pin EPS cable near the CPU socket | Easy |
| Shorted front-panel power button or case wiring | Jump-start the PSU with the paperclip test; if it runs, the fault is outside the PSU | Medium |
| Genuine PSU failure (blown internal components) | Paperclip test fails, burnt smell, or audible pop before death | Replace unit |
Fix 1: Check the Wall Outlet, Power Strip, and AC Cable
What causes it
A tripped breaker on the circuit, a switched-off or surge-damaged power strip, or a cracked AC cable can starve the PSU entirely. Surge protectors fail silently — the outlets still look fine but pass no current.
How to check
Plug a lamp or phone charger into the exact outlet you’ve been using. If it works, test the same device through your power strip. Inspect the PSU’s AC cable at both ends for bent pins in the C13/C14 connector and check for a loose fit where it enters the PSU.
What to do
Plug the PC directly into the wall, bypassing any strip or UPS. If it boots, replace the strip. If the outlet is dead, check your breaker panel and reset any tripped breaker. If the outlet works but the PC doesn’t, swap in another IEC C13 cable — most monitor or appliance power cords use the same connector.
How to undo it
Nothing to undo — reconnect your surge protector or UPS afterward if you want the protection back, once you’ve confirmed which component was faulty.
Fix 2: Check the PSU Rear Switch and Voltage Selector
What causes it
The rocker switch on the PSU’s rear panel is easy to bump off while routing cables or moving the case. On older or import units, a red 115V/230V selector slider set to the wrong value trips overvoltage protection or prevents startup entirely.
How to check
Look at the rear of the case where the AC cable enters. Confirm the rocker switch shows “I” (on), not “O.” If there’s a voltage selector window, confirm it reads the correct value for your region — 115V in North America, 230V in Europe and most of Asia.
What to do
Flip the rocker switch to “I” and press the case power button. If a selector was wrong, unplug the AC cable first, slide the selector to the correct value, then reconnect and power on. Never move the selector while plugged in.
How to undo it
Flip the switch back off when transporting the PC or working inside the case — that’s good practice anyway.
Fix 3: Perform a Power Drain to Reset Protection Circuits
What causes it
Modern PSUs have latching protection circuits — over-current protection (OCP), short-circuit protection (SCP), and over-voltage protection (OVP). A momentary short or power spike can trip them, and the unit stays off even after the fault clears until the standby power drains.
How to check
If the system twitched briefly when you pressed power — fans nudged, then died — or if the problem started right after installing new hardware, a tripped latch is likely. This behavior is the signature symptom.
What to do
Switch the PSU’s rear rocker to “O” and unplug the AC cable. Press and hold the case’s power button for 30 seconds to drain residual standby power from the motherboard capacitors. Wait two to three minutes, reconnect AC, flip the switch to “I,” and power on.
How to undo it
No changes are made to the system, so nothing to revert. Your BIOS settings are preserved because the CMOS battery holds them during the drain.
Fix 4: Reseat the 24-Pin and CPU (EPS) Power Connectors
What causes it
The 24-pin ATX connector or the 4/8-pin EPS cable feeding the CPU socket can work loose during a move or was never fully clicked in during a build. A missing EPS connection makes some boards refuse to power on at all.
How to check
Power off and unplug. Open the side panel, press the release tab on the 24-pin connector, pull it out, and inspect for bent or pushed-back pins on both the connector and the motherboard header. Do the same for the EPS connector at the top-left of the motherboard near the CPU. Check that modular cables at the PSU end are fully clicked into the correct sockets — EPS is not interchangeable with PCIe on most units.
What to do
Reinsert the 24-pin connector straight down until the latch audibly clicks. Reinsert the EPS cable firmly. On semi-modular units, verify the cable labeled “CPU” or “EPS” runs from the PSU’s CPU socket to the motherboard’s EPS header, and that a PCIe-labeled cable isn’t in its place — forcing the wrong one can damage components.
How to undo it
Press each connector’s release tab before pulling; never yank by the cable. No lasting changes are made.
Fix 5: Run the Paperclip (Jump-Start) Test to Isolate the PSU
What causes it
You need to know whether the PSU itself is dead or something downstream (motherboard, front-panel wiring, a shorted component) is preventing startup. The jump-start test forces the PSU to run with no motherboard attached.
How to check
Unplug the AC cable and wait two minutes. Disconnect the 24-pin connector from the motherboard. On the PSU end of that cable, locate the single green wire pin (PS_ON) and any adjacent black wire pin (COM/ground). Bend a paperclip into a U shape and insert one end into the green pin’s socket and the other into a black pin’s socket. Reconnect AC, flip the switch on, and observe.
What to do
If the PSU fan spins and the unit stays on, the PSU is functional (at least at idle) — the fault lies with the motherboard, power button, or case wiring, so continue to Fix 6. If the fan does not spin, twitch once, or the unit shuts off immediately, the PSU has failed and should be replaced. Remove the paperclip and reconnect everything afterward. This test runs the PSU with no load, so don’t leave it jumped for long.
How to undo it
Switch the PSU off, unplug AC, remove the paperclip, and reconnect the 24-pin cable to the motherboard until it clicks.
Fix 6: Test the Power Button and Front-Panel Wiring
What causes it
Case power buttons fail more often than people expect — the momentary switch inside wears out, or the thin PWR_SW wires from the case to the motherboard’s front-panel header are loose or on the wrong pins.
How to check
With the PSU switched on and AC connected, locate the front-panel header on the motherboard (labeled F_PANEL or JFP1 in the manual). Find the two pins for PWR_SW. Briefly touch a flathead screwdriver across both pins — the same contact the button makes.
What to do
If shorting the pins starts the PC, your power button or its wiring is faulty. Reseat the PWR_SW connector on the header (polarity doesn’t matter for this switch), and inspect the cable run for pinches. If reseating doesn’t help, contact the case manufacturer for a replacement front-panel assembly, or temporarily wire an external momentary switch to the header. Some motherboards also include an onboard power button — check near the bottom-right edge of the board.
How to undo it
Pull the connector off the header by gripping the housing, not the wires, and restore your original layout per the motherboard manual’s header diagram.
Fix 7: Disconnect Non-Essential Hardware to Rule Out a Short
What causes it
A shorted fan, a jammed pump, a faulty RGB controller, or a damaged drive can pull a rail down instantly, tripping SCP before the system even POSTs. This often appears right after adding new hardware or rerouting cables.
How to check
Think back: did this start after installing a component or rearranging cables? Look for a SATA power cable pinched against a sharp case edge, or a fan with frayed wires near a spinning blade.
What to do
Unplug the AC cable, then disconnect everything non-essential: all SATA power cables from drives, all case fans except the CPU fan, any RGB strips or controllers, and discrete GPU power cables (leave the GPU seated if your board requires it for POST). Reconnect AC and try to power on. If it starts, reconnect devices one at a time, powering on after each, until the culprit kills the system again. Replace that component.
How to undo it
Reconnect each disconnected cable, making sure the 6/8-pin PCIe power to your GPU is fully latched before gaming.
Fix 8: Reset CMOS and Check for Motherboard Standby
What causes it
A corrupted firmware state or an ErP/deep-sleep setting combined with a dying CMOS battery can leave a board unresponsive to the power button, mimicking a dead PSU.
How to check
Look at the motherboard when AC is connected: a lit standby LED or glowing debug display means the board receives standby power and should respond to the power button — pointing away from the PSU. A completely dark board after Fixes 1–5 suggests motherboard trouble.
What to do
Unplug AC, remove the coin-cell CR2032 battery from the motherboard for five minutes, then reinstall it with the “+” side facing up. Some boards have a CLR_CMOS jumper — short it per the manual while unplugged. Reconnect and power on. If the board had ErP Ready enabled (found in BIOS under Advanced > ACPI Settings on many boards), disabling it restores normal standby behavior.
How to undo it
A CMOS reset clears BIOS settings to defaults, so re-enter BIOS (usually Del or F2 during POST), re-enable XMP/EXPO memory profiles, set your boot drive order under the Boot menu, and save with F10.
If Nothing Works
If the paperclip test fails, if you smelled burning or heard a pop before the failure, or if the PSU trips protection instantly even with everything disconnected, the unit has internally failed and must be replaced — never open the enclosure to attempt a repair. When choosing a replacement in 2026, size it with roughly 30–40% headroom above your system’s expected draw, and favor units with a good warranty track record. Before installing the new unit, note your current cable routing and take photos; then use only the modular cables that shipped with the new PSU, since pinouts differ between brands and models and mismatched cables can destroy components. If the PSU tests good but the board stays dead through Fixes 5–8, the fault has moved up the chain: test with another PSU if you can borrow one, then evaluate the motherboard for repair or replacement, and check whether your board is still under its manufacturer’s warranty (commonly three to five years).
FAQ
Can a power supply fail without any smell, noise, or visible damage?
Yes. A single failed startup circuit or a blown surface-mount component can kill a PSU with no external signs. The paperclip test is the fastest way to detect this kind of silent failure.
Is the paperclip test safe for my PSU and components?
It’s safe when done correctly and briefly, because the motherboard and all components are disconnected during the test. Only bridge the green PS_ON pin to a black COM pin on the 24-pin connector, never touch any other wires, and don’t leave the PSU running unloaded for extended periods.
Why does my PC twitch for a second and then turn off?
A brief fan spin followed by shutdown is the classic signature of a tripped protection circuit or a short somewhere downstream. Try the power drain in Fix 3 first, then disconnect non-essential hardware in Fix 7 to hunt the short.
How long should a power supply last before it fails?
Quality units are typically rated for 5 to 10 years of service, and many carry warranties in that range. Heat, dust, and running near maximum load shorten that lifespan, so periodic cleaning of intake filters and PSU vents helps it reach full life.
