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My computer cut out one day (all the lights, etc were still on, but no activity) I replaced the power supply, but now it starts up for about 5 seconds and then shuts off. . .any ideas?

I've checked all the connections, nothing seems to be 'fried', so any input will be greatly appreciated.
Thx in advance.

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This thread points toward a power-failure that survived a PSU swap. described a brief power-up then an immediate shutdown, and correctly noted that power delivery problems can damage other parts. The next steps are about isolating which piece is failing — the supply, the board, or the CPU — using safe, cheap tests before replacing parts.

Start with a true minimal bench test: unplug mains, remove the case from the motherboard, then connect only the CPU (with cooler and fan), one known-good memory module, and the motherboard power connectors. Do not connect drives, add-in cards, or front‑panel USB. Try powering the board from a different, known-good ATX supply if available. If it still dies fast, the problem is likely on the motherboard or CPU; if it stays up, something you removed is likely causing the shutdown (add pieces back one at a time to find it).

Check the PSU itself: some units will sit up briefly then shut down when an internal protection (OCP/OVP/short detection) trips. A bench PSU tester or a multimeter under load will reveal bad rails. Also inspect both the PSU and motherboard for bulging or leaking capacitors, scorched components, blown MOSFETs, or a burnt smell. Make sure the CPU 12V/4‑pin connector is fitted firmly and that no standoff or screw is shorting the PCB.

If a vetted PSU and minimal bench still fail, suspect the motherboard or CPU and plan for parts swaps or professional diagnosis. For background on the ATX power-good signal and why a PSU can allow a short spin-up then cut out, see the ATX specification overview: ATX (power supply specification).

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Member Avatar for Chaky

Did it behave the same with old PSU? Can you list your configuration (and old and new PSU's wattage)?

Member Avatar for ChanTicO

no, with the old psu it wouldnt fire up at all. there was a little led light on the motherboard that was on. . .thats about it.
the dead psu was a 300 (tested w/ another 300 psu from the machine i'm posting this, and i got the same issues as the new one, which is 350 watt)

it's an amd2400 processor on an asus motherboard.(A7N8X-X)
1.25g ddr400 memory (3 sticks)
nvidia fx5600xt vid card


Again, one day i noticed the light on the front of the machine was on, but the usual humming of the system was missing. I hit the pwr button, and the lights went out. .but in trying to restart it, nothing happend.

Replacing the PSU yielded favorable results, however around the time I should be hearing the 'magical' beep just before initializing, it shuts down. I dont see any damage, and i've troubleshot various components (trying 1 stick of ram at a time, etc. .) and I still cant get it to stay on.

Member Avatar for Chaky

300 w is way too weak for the machine like that. 350 w barely makes some sense. You should find PSU 450 w or more to test.
No wonder 300 w fryed. It was giving 110 % all the time.

Lack of power might done some damage to the system. CPU's most wournable there for it recives 2 or more different voltages. If any of those voltages went up (in the moment of PSU frying) be sure it is FUBAR.

Member Avatar for ChanTicO

so if it did fry the cpu, ( i looked at it, and nothing was physically wrong w/ it) could the motherboard be screwed as well?

Member Avatar for Chaky

Yes, but usually the CPU is first to go. They both can be fryed. And it takes 1.5 V to fry the CPU, so it won't be anything visible to the naked eye.

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