I didn't go ahead with formatting and reinstalling Windows over the weekend. I did solve my random crash problem by reinstalling Norton Internet Security - the crash that occurred after that was caused by something entirely different. I still might go ahead and format and reinstall this weekend, though - just to make sure.
I ordered a new PSU yesterday. In addition to being noisier than I'd like, I'm none too happy about my current PSU's ability to cope with my machines power needs (it sounds very strained when running intensive applications or games and it shouldn't be). The new one should arrive in time for installation over the weekend.