one suggestion is to have a clean install at every bootup but not to everyones taste but least its nice and bright and clean every day
You would use something like ROLLBACK that auto rolls back all software/changes to the system drive or drives specified on restart /bootup
the training center i work for has this on their systems to avoid the hassles of fixing machines every single day they just revert to their original status upon reboot
any drives not set to ROLLBACK are left as is
other than this if its a store bought system you usually get a set of restore disks to revert the drive to shop fresh clean
or as poacher says above FORMAT C: drastic sure but you get the cleanest drive outta the 3 ideas