Pavilion 7940 - continuously blinking power light

I'm working on someone's Pavilion 7940, which is experiencing general
slowness and random crashes (XP blue screens usually with a 8e stop
error).

Generally, those symptoms would indicate a hardware problem to me, so
I'm trying to narrow it down a bit, although the user had an enormous
amount of spyware on the machine to begin with, which is making things
a bit difficult to properly diagnose.

I've noticed that most times after a reboot the system will power up
OK, but the power light blinks continuously. I've searched and I can't
find a 7940 system manual on HP's site, so I'm not sure what that means
exactly. Usually something blinking like that would indicate a fault
of some kind - anybody know what it means or where I can find that out?

I've also ran MemTest86 on it (which boots from a minimalist version of
Linux), which didn't find any memory errors, but each of the tests took
a very long time to run, so I'm thinking there might be a memory
problem, or possibly a damaged chipset or maybe even processor...

Thanks,
Glenn