I left my computer unattended, and when I returned, Windows had shut down, my monitor was in energy save mode, my external hard drives had shut down, but the computer would not shut off or reboot. The only way I can power down is with the PSU switch. As soon as I turn the switch back on, everything turns on and I cant reboot. I have had to bring my old computer out of retirement in an effort to find a solution

Is this a fault with my PSU, or is there more. Any help would be appreciated.

Thanks
RLL

I experienced a similar case before. The culprit was the memory. Try to check your memory if one (I'll assume you have more than one) of your RAMs is defective. If the hardware is all fine, the OS is probably the cause.

Answer here:

http://forums.hardwaresecrets.com/computer-dead/3245