I have been having random lockups on my machine. I do not know if this is a hardware or software problem.

When I get locked up, I can not pull up a terminal by <ctrl><alt><F2>. I have to power it down by the power button.

Could someone point me which log I should be looking at to find the problem?

Thank you!
Extra info: Restricted driver in use - nvidia graphics. Compiz in use. V9.04