I got 2.5 year old system here what crashes randomly, it can happen at night when torrent client is working(then monitor stays in stand-by mode although PC is working), it can happen while playing StarCraft(1998 year game), it can happen while browsing the web. Crash turns PC completely unresponsive, keyboard and mouse won't work(not even num lock and such keys), audio will stop playing.
I have noticed that sometimes booting OS will get stuck at 'loading kernel modules...' and sometimes PC speaker won't beep.
Log files have no entry about the crash.
Issues started happening around week ago. No hardware chances since then.
Temperatures are relatively high, but nothing over the limits and they've been like this for a while.
So far I have:
Clean installed operating systems - Debian Testing, XP Pro
Done memtest - all good
Done seatools test - all good
Replaced HDD - no change
Replaced PSU - no change
Motherboard and graphics adapter are fairly new if that matters, maybe 3 months at most.
For some reason I can't edit my post...
Booted PC with only essential parts: mobo, cpu, cooling, psu, hdd, 1 stick of ram, video card - still crashing. But I noticed one weird thing - CPU fan was changing speed