Quote Originally Posted by Xaven
Ctrl + Alt + Delete, then go to the Processes tab, and make sure you close (End / End Tree) everything that's un-needed for windows to run correctly. (That includes everything with capital letters.) There's so much crap running on most people's compy's and they don't even know it.
This is probably your best bet. Once you get your computer down to the core processes, run your virus scan, then spyware, then defrag, etc... It is very possible that you have a virus that prevents your computer from updating, or a conflict in programs or spyware is causing your computer to act up. By closing all unnecessary processes you're giving your computer a better chance to clean itself up as there is less of a chance of other programs and such interfering.