Okay, I don't know exactly what cCleaner took off--nothing on the list looked unusual; it was mostly leftover cruft from programs I've uninstalled over the last couple of years--but my computer's already running better, and I was able to get back on my own user profile. Things seem to be running better, too. The test will be if I have another crash tonight, but I guess I'll keep the computer running until I have one, just to see how long it takes. In other words: thank you, that was an awesome suggestion.

(I also ran Process Explorer, but I can't figure out how to read it quite yet.)