Urgent help with Vista. Laptop will not run properly for long amounts of time under anything but Safe Mode?

Problem began earlier today when I woke up my laptop to type out a blog post, while listening to music on foobar2000 which had the scheduler plug-in. Everything hung, and after a while, I received an error (silver font on black background, a la command prompt) informing me that "no operating system [was] found." I rebooted back into regular mode, and went about all my activities, only for the laptop to hang a few minutes in. This repeated a number of times, only for me to grow frustrated and boot my laptop into safe mode with networking enabled. My laptop ran fine under this, I downloaded avast! and ran it, and dealt with the trojan virus that it'd discovered. While leaving it to run, I left for a brief nap, and returned to find my computer had automatically rebooted itself back into regular mode. Believing the problem was fixed, I opened up Firefox, Windows Live Messenger, and AIM in quick succession (as has been done before, to no consequence). All three programs worked momentarily, but my computer hung and I had to do a manual reboot. I'm back in normal mode, and everything seems to be going fine so far (maybe 20 minutes in), but I've not started up either AIM or WLM. I do not recall starting either of these applications prior to one of the previous freezes, so I'm not wholly convinced that one or either is to blame.

I've had suggestions for a system restore and antivirus scan and defrag. I'd really not like to run a system restore unless I really have to, so any other ideas while I'm waiting?