Hi there,Welcome to the forums.
You could start off with a registry clean up as this often cures loads of errors from left behind registry keys etc.Things left behind when software etc is removed,Try a search of the forums for regcleaner that will remove unnecessary registry entries.For a thorough clean up of your hard drive then i would recommend buying the winoptimiser suite from www.ashampoo.com it is relatively cheap and does a fantastic job.