I would still suspect the PSU as a fault even though you've already swapped it out once. the problem maybe a 2ndary one. The mtrbd. could be acting out. I suggest you google for "bad caps" examples. Use that to check and verify the mtrbd. out. Not only that but the mtrbd. could have faltered and it "eventually" taking out the PSU sooner or later. -OR- you added to the PC more items/devices and it is too much for the PSU to handle. if you've replaced the PSU with the same wattage rating as before, it got hosed.
You want help. provide details. You gave no clue to what your PC, it does matter.
tada -----Willy 
Hi Guys,
Hope someone out there can help. I had an intermittent problem with my PC (Vista) a month or so ago. The PC started powering down on it own (power would just cut out), although the light on the mobo was always on. It did this at random points, sometimes when windows had loaded, sometimes before the BIOS had started.
I took the entire machine apart, and then went through diagnosing each part (RAM,HDD,swapped out graphic cards etc), still to no avail. So I eventually changed the PSU, and it worked! It's been running ok for a month, and now the same issue has happened again, except now if it shuts down, it will suddenly start to power up on its own at random points. CPU temps are normal.
Feels like a short or electrical fault, but cant quite work it out.wondering if the power button on the case could be faulty? Anyone have any ideas?
Thanks
Chowhound
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