Well, I'd heard of perfmon, but I really never checked into how to use it. This article suggests running
from the start menu or a command prompt. After you do that, it will collect up data from the past few weeks and present it in a graph form. Mine looked like:
That's really cool! So you have a day-by-day look at what your system has been doing, and where it's been failing. Clicking each of the red x icons gives you a look at what failed on that particular day. The blue information icons tended to be system or application updates. You can see application crashes and other things that may be affecting your system.