ye do disk defragment thats good. get a couple of programs to, i use tuneup utilities (1 click maintenance and clean disk), CCleaner, PC Rescue, Reg cleaner, Registry mechanic ect ect... and make sure you get spyware and virus removers like avast and spy sweeper, spybot search and destroy. those programs will make your computer more efficiant and more reliable and clean junk like you wanted. btw there not all free but in my opinion a good investment.
but formatting your hdd will always be the best way