Recently my PC has started randomly restarting itself. It has got slightly worse over the passed week. In Windows 7 on my main HDD it restarts every ~20 mins, in Ubuntu 11.10 on my secondary HDD it only restarts every ~6-8 hours, so I'm having to use Ubuntu if I want to get anything done.
The main HDD is partitioned and I've re-installed Windows already to see if that helped, I also re-installed Ubuntu, that didn't change anything either. When I installed the proprietary driver for my graphics card (an old 7800GTX) in Ubuntu it began to restart more often so I just run it without. In Windows I uninstalled the driver for the card and it still restarted itself just as often.
When it restarts itself what I mean is the power appears to completely cut out as if the system is off, it then attempts to restart itself 3 or 4 times failing and cutting out before successfully starting up. I checked all the temp monitors and the hottest it gets under load is ~78 on graphics and ~65 CPU.
I'm guessing it's caused by the power supply dying? I can't think what else it might be, but some suggestions might help find out what it is, I don't really have the money to go replacing my power unit to find that it's some other hardware that needs replacing!
Specs:
PSU: 500W
HDD1: 1TB - Windows 7
HDD2: 160GB - Linux Ubuntu 11.10
CPU: Intel Core 2 Duo 3.0GHz E8400
RAM: 2GB
Graphics: Nvidia GeForce 7800GTX