Time for a clean install, Windows accumulates all sorts of junk over time, so It's a good opportunity for a clear out.
Make sure you've downloaded all the drivers you need before you start and you have them safe on a disc. Backup up all your data - twice. If you have any games, back up your game saves. If you have any skins or themes back those up too. And then there's e-mail...
You should be back up and running, lean and clean in no time at all