Get rid off programs that u don't use. Especially those , that came with it.
Use http://www.ursoftware.com/ , its best to remove unwanted soft, that wont go uninstall with windows uninstaller.
Unlike windows uninstaller, this removes most traces of that those programs. So it keep your PC running smoother.
Look, when u start PC, junk or programs that u don't need at the moment(printer soft,iTunes...) tend to start up with system - that's your slowdown.
Download free and great tool CCleaner http://www.filehippo.com/download_ccleaner/ - if u already don't have one, u should have one. Thats your PC maid - it cleans and repairs general registry issues and u can control the start up programs too.
Or u can get SSD drive like Vertex2 and speed up things dramatically.