Sorry about the delay - I don't think that the system will notify me of edits to existing posts - and I've been traveling for the last couple of days.
I'm starting to think that this is a hardware problem - and most likely it's heat related (that's just a guess). Try opening the side of the case and pointing a house fan in there. Continue to do what you normally do with it. Does that make things better?
My best guess at this point is that there's a problem with your system - and that only certain actions affect it. If the fan thing above doesn't work, we'll have to try some other tests (such as Prime 95, a video stress test, and maybe a system stripdown to see if that affects it)
Normally, at this point, I'd be suggesting a wipe and reinstall of Windows (and am wondering if it'd help out here). A complete wipe of your hard drive, then install Windows, then update Windows from Windows Update, then ensure you update any missing drivers
in Device Manager. If, after this, the system still freezes, then that tends to confirm the suspicion that it's a hardware issue. Unfortunately, the random nature of the freezing will make it difficult to diagnose through a system stripdown.