have you been doing regular maintenance to your PC like spyware and adware scans, disk defragmenting, running disk cleanup, running virus checks, removing unnecessary programs/files, cleaning up startup processes, etc? These are all things you need to stay on top of in order for your computer to continue functioning properly. I suggest you attempt to do some of it if you haven't or a fresh install of windows will be required (i know that will be difficult seeing as you don't have the windows discs but that might be your last option).
Another option you can try is doing a system restore to the earliest date available and starting from there to clean up your computer.
Killing under the cloak of war is no different than murder
Kein Alkohol ist auch keine Lösung!