The PC starts itself after a power cut, then dies
Why does my PC turn on after a power outage then immediately turn off again?
Written by The CommonFixes team · fact checked by CommonFixes review desk
Last updated
Short answer
Two separate things are happening. The board is set to restore power after an outage, which is why it starts on its own. The instant shutdown afterwards is the protection circuit in the power supply cutting out, usually because the surge on the way back damaged it, or because the board is still holding a bad power state. The quickest thing to try first: drain the standby power — Switch the socket off and pull the cable out. Hold the case power button for thirty seconds to bleed the stored charge from the board and the power supply. Plug back in and try once. Do this before anything else, because it clears a latched protection state. Most people are done in about 25 minutes.
Full walkthrough below: 6 steps for Windows, rated careful.
Sounds like this
- •The tower powers itself up as soon as the electricity returns
- •It runs for a second or two, then shuts down
- •It may repeat the cycle over and over
Why it happens
Two separate things are happening. The board is set to restore power after an outage, which is why it starts on its own. The instant shutdown afterwards is the protection circuit in the power supply cutting out, usually because the surge on the way back damaged it, or because the board is still holding a bad power state.
Work through these in order
0% done- 1
Drain the standby power
Switch the socket off and pull the cable out. Hold the case power button for thirty seconds to bleed the stored charge from the board and the power supply. Plug back in and try once. Do this before anything else, because it clears a latched protection state.
- 2
Move the PC to a different socket, without the surge board
Plug directly into a wall socket. A protection strip that took the hit during the outage often clamps down afterwards and delivers unstable power that trips the supply. If the computer behaves on the wall socket, replace the strip.
- 3
Test the power supply on its own
Switch off, open the case, unplug the twenty four pin connector from the board, and bridge the green wire to any black wire with a bent paper clip while the supply is switched on at the wall. If the supply fan does not spin, the supply is dead. If it spins, it may still be weak under load, so treat this as a rough test only.
- 4
Strip the machine back to the basics
Disconnect all drives, extra cards and case fans. Leave board, processor, cooler, one stick of memory and the power supply. If it stays on now, add parts back one at a time. The one that brings the shutdown back is the one drawing more than it should after the surge.
- 5
Decide how it should behave after a power cut
Once it starts properly, enter the firmware with Delete or F2 and look for Restore on AC Power Loss or After Power Failure under Power or Advanced. Power Off is the safest choice for a home PC, since it stops the machine starting into an unstable supply next time.
- 6
Look for damage you can see
With the machine unplugged, check the board for capacitors with domed or leaking tops, and sniff for a burnt smell near the power supply. Either sign means the part is finished and running it further risks the rest of the computer.
If none of that worked
Swapping in a known good power supply is the quickest way to settle this. If a healthy supply still shuts down straight away, the fault is on the board and needs a technician. Use an uninterruptible power supply afterwards to prevent it happening again.
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The CommonFixes team
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This guide was last updated on 15 August 2026. If a step no longer matches what you see on screen, tell us on the contact page and we will test it again.
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