I cannot spend 2-3 hours/day rebuilding hard drives like this. I'm contemplating doing a bare-metal installation (again!) on one of the three 250GB drives just to see if doing that (and downloading the inevitable mountain of updates) before installing any of my software will do any good. There's enough stuff on my machine that there's no telling exactly where the problem lies.
I'm doing some other things like making a fresh copy to DVD of all of my program and driver installer files, which I'll need in particular if I have to reinstall everything from scratch again. I'm also turning off automatic updates until I isolate this problem, because it seems highly likely that something in the current batch of updates is contaminating my machine.
Update, 12:30: Corrected the point where the computer goes to a blank screen: it's right after the power-on screen but before Windows actually boots.