well for starters, go to www.ccleaner.com an download the free version, it will clean it right up. then defragging is done by doing this, click on start in bottom left, then all programs, then accessories then system tools, then defragment.. when your computer uses memory it kind of saves bits of files here an there, defraging it just puts them all together as you would expect them to be in the first place.. if he's been looking at porn you may have a virus mate..