make sure you have some space left in your hard drive. Your computer gets slow if there isn't much space left in your hard drive.
also, you don't have multiple anti-virus installed, right? That will slow down your computer significantly, and different AV will conflict with each other, and might result in none of them working correctly, leaving you more vulnerable than having one.
delete programs you don't need in control panel, do a disk clean up...can't think of anything else