As I said, I don't know that it will help, but Scandisk and Defrag only make sure that the files that are there are in good shape. The other routine, Disk Cleanup, actually gets rid of some of the excess (useless) files, and might help your speed.
Restore is a pretty drastic step. It usually gets rid of EVERYTHING you may have added to your drives. Backup everything first, if that's what you decide to do.
If you're going to restore the programs, of course you don't necessarily need to back them up. You should try to get all of your data off the hard drive though.
In Start - System - Add/RemovePrograms you can sometimes "overlay" a restore of corrupt Windows files without reformatting, but some vendor's CDs do a hard drive reformat when you do a restore. That erases everything.
Wish I could offer more help, but I'm afraid I haven't seen anything that really resembles your basic problem with McAfee.