This is kind of a scorched earth approach but it’s what I do, rather than kind of nickel and dime the thing with clean up programs and tweaks. And it’s a major pain in the ass because you have to reload all your applications and set everything up again but… back up and/or transfer your data to disks or an external hard drive then reformat the thing or run the recovery disks. It should run pretty well after that. Works for me, but like I said, kind of a scorched earth approach, not for everyone.