I've seen that after folk update drivers or use registry cleaners. There is no single cause or cure. That is, the road back is pretty rocky or uncharted. Lesson? Don't update drivers or use registry cleaners.
I have a weird problem: the screensaver and computer sleep modes will start the first time the computer is booted up but will not start after that. In Power Options, I have the screensaver set at one minute and the computer sleep set at one hour. (I checked regedit and ScreensaverActive = 1).
Using Windows 7 Home Premium with automatic updates. Any ideas?