Hardware lockup - need suggestions for diagnosing

[Larry Cook]

I'm trying to diagnose my friends Dell Latitude C600 P3 @ 800MHz.  It 
just locks up w/o rhyme or reason.  Ctl-Alt-Del won't work when it locks 
up, so that, along with the fact that it happens with two version of 
Windows and four different Linux Live CDs makes me think it's a h/w 
problem.  It also seems to happen more quickly when cold.  (Isn't it 
usually the other way around?)  It hardly gets very far in the boot 
process when cold.  Once it's been on for a while I can get the OS 
booted and can do things, but it just locks up without any apparent 
relation to what I'm doing, or even when I'm not doing anything. 
Sometimes it just powers off.  I'm running on AC, no battery installed.

I've downloaded the Dell Latitude C600 diagnostics ran them for hours 
without a problem.  There are two RAM DIMMS, so I've tried with only one 
and then the other and in each of the slots.  So it doesn't seem like a 
RAM problem.  I've disabled Power Management in SETUP, I've tried w/ and 
w/o a mouse attached, and w/ and w/o the network connected.

Should it just be recycled or are there some ways I can diagnose the 
problem?  Any good diagnostic programs I can run?

Thanks,
Larry