[Techtalk] Determining Hardware Or Software Problem

[Kylie Willison]

I don't have lots of details but I'm trying to work out if
this is a hardware or software problem.

Fresh Ubuntu (hoary) install worked fine for about 3 or 4
months on a secondhand computer.  Now according to the owner
it's freezing after login then reboots.  Even turned itself
on in the middle of the night once.  Yet I've been able to
boot and login fine.  So far I've only tried it once.

I'm not really sure where to start looking first.

TIA
Kylie