I know it's an old post, but I experienced this very thing over the weekend. And almost jumped the gun and start deleting everything, but hold on a sec. This all worked fine the day before yesterday, so what else has happened since then? Now I'm not saying that Microsoft is to blame, however, my hard drive is a scrambled mess from... oh, different thread.
Anyway, all I'm saying is that even a slight modification to your system (something as minor as a Windows version upgrade thrown at your system without warning) could have a ripple effect elsewhere. I tracked down the windows.old folder, deleted completely from my hard drive, rebooted and everything has been fine since.
Don't misunderstand me, I'm not discounting anything that has been posted here or saying anything is wrong with any of the suggested solutions. I am merely throwing my experience out on the table. So, if you experienced any similar computer-based update or upgrade, check out the .old folder. But research it a little more before just deleting it. I did and my experience here and what I did was really abbreviated for the sake of not boring everyone to death.
