When I built this PC back in February, I had an old 500 GB Maxtor SATA drive sitting around that was about 2-3 years old. I never used it, never even opened it, and figured it'd be great. I've posted a lot about my system crashing and having errors like not being able to install MS office, and I think I figured out why. Apparently the old HD, while not showing any errors in checkdisk, was just not up to modern requirements.
I replaced my old Maxtor with a 500GB Seagate drive today (I don't need 1TB+ yet b/c I have another external 500GB), re-installed windows and it works perfectly.
That's good that you got it figured out.