[Azselendor]

Things to try:

1.) boot into safe mode and see if it happens.
2.) create a new user profile and log into that and see if it happens
3.) Roll your system back and see if that fixes it.
4.) Check for dust and lint buildup inside the CPU (sounds like this isn't an issue if you were checking for power)
5.) check cable connections for a loose one
6.) check msconfig via the run start menu item for programs.

My computers periodically lock up at random due to 5 programs I have that love to piss away memory.
1.) Firefox 2
2.) Safari (leaks memory like the ocean leaking into the titanic)
3.) Open Office's background soffice.bin process
4.) Linksys wireless monintor program.
5.) google desktop