PC shuts down intermittently
I have troubleshooted a PC which boots up and goes as far as the Windows Splash screen and on at least one instance pass the Windows logon screen. After a couple of minutes it loses power, like you would expect in a powercut. I changed the power supply and used a working 12V ATX power supply to test if it was the PSU. On replacing the PSU I got the same problem. Now, I put the PSU back into it's original PC and the PC won't boot. It powers on and the PSU fan and CPU fan spin but it doesn't start the bios program and there is no output on the screen. I'm getting exactly the same result on the problem PC. They both have AMIBIOS. The original working PC doesn't beep to indicate passing the POST. While the problem PC gives one beep but on pressing the DEL key does not enter setup.
My question is, could a faulty component, in the PC which was shutting down erratically, have damaged the PSU of the working PC? I had eliminated the possibility of malware or virus by doing scans on the hard drive. I also removed the RAM from the PC and tested this in a working PC. Has anybody got any suggestions of what to do next?