Computer freezes when not operating

I have possibly the same problem. The mouse works but nothing else responds. I have the power switch mapped to suspend and pressing that, waiting for power down and pressing it again restarts the system where I left off with all working normally. I changed the motherboard as I thought there was a problem with interrupts and I added additional memory - moving the old ones to the higher slots - but the system behaves the same way. The processor is not running hot and booting from different disk drives shows no improvement. Could it be a power supply problem or a faulty processor? Try the suspend and resume approach to see if you can at least save your work before rebooting.