have you ever reloaded windows? I personally do it every 6-9 months just because you inevitably have some corruption within the system files. If that doesn't appeal to you then you could run setup and do a windows repair instead. I'd still advise backing up your system before you did that though.
I also like this program which cleans your registry and will also clean startup items. I've used it for a while now and it is a nice small program that does a good job preventing things you don't want from installing.
http://www.yac.mx