For example Electrolytic Capacitors are found in old (and new) machines that need replacing. Have you inspected yours?
And then we have heat sink compound. Have you replaced such and while doing so cleaned the machine?
BEWARE those older Socket A machines. Savvy repair shops will reject those at the service counter.
I have a 9 1/2 year-old PC which will sometimes stop working when I'm using it. Let me define "stop working" - the monitor goes black, and I can verify that programs running on the PC have crashed. Yet the lights on the PC remain on. If I try to turn the PC off using the push-button switch, nothing happens. The only way I can turn off the PC is to unplug it. Then, if I try to power the PC on, it will not do anything - for about a day or so. Then it will start up.
The interval between the PC crashing and the time I can turn it on next makes me think of a capacitor that needs time to discharge, but that's just pure speculation.
The most recent time the PC stopped working, it had been running all night with a light load, but crashed when I was browsing internet pages.
So, is this likely to be a bad power supply problem or a bad motherboard problem?