I'm having a problem with my desktop whereby it sometimes resets itself semi-randomly. For example, I'll switch it on, it'll boot an OS and shortly after getting to the desktop it will immediately reset with no warning. The time isn't consistent - sometimes it does it before reaching login.
I'm pretty sure it's not an OS thing; have tried Ubuntu and a Windows install and both exhibit it. It also doesn't appear to be heat-related because sometimes it appears to be able to "get past" it and will then run stably even under load; if anything it seems to be worse from a cold start.
My gut feeling is some kind of power issue but I'm clutching at straws a little. Any suggestions on how I could go about testing it or trying to narrow the problem down would be appreciated.
The machine is four years old now so while I can replace components if needed, it's not worth enough that I'm comfortable buying new parts without being pretty confident that they'll fix the problem.
Thanks in advance for any help :)
Edit: Okay, the motherboard is a MSI K8N SLI; CPU is an Athlon64 X2 4200+. Has one video card, a GeForce 7800GT. 1GB RAM, not sure of brand; 3 hard drives, two SATA and one PATA. Flashed motherboard to latest BIOS some time ago.
Edit the Second: I thought I'd narrowed it down to the PSU for a while, but then it recurred again. I ended up pulling everything out but CPU, RAM and motherboard and it still seems to be stuffed (if anything, it's gotten worse in the last couple of days). I assume it's one of those three components, but the machine is old enough that I don't really want to spend money replacing any of them. So thanks for everyone's suggestions; much appreciated!