Do a disk defrag and disk cleanup (windows). Do a spyware scan (Spybot Search/Destroy works well) and a virus scan (i like Avira). That should help..

You may just have to reinstall windows if it's really bad. It's been 3 years for me since I've last done a clean start and I need to do so sometime soon.

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1985 CA 300D Turbo , 213K mi