Reformatting is just resetting your HDD to be completely wiped empty. No OS, no files, nothing. IMO it should only be used as a very last resort, if then. I had a similar problem just recently which had been there for months. Both Spybot and Adaware couldn't do anything about it. I suggest getting antivirus programs like Avast! Antivirus and AVG Free Edition. Update them both and run them. I forget which it was, but one of them said that there was soemthing it couldn't delete and asked to run before the OS started. I said yes, that blue screen it shows when it does the disc check showed when I rebooted and it started checking for viruses. It found stuff, I got rid of it and now my PC runs fine. Also, it is suggested that you run them in Safe-Mode to limit what processes are running.
Also, if you want to speed up your HDD, you should defragment it. What that does is it basically cleans things up and moves them around to be more efficient. The things on your drive are stored physically on a disc. There's a little head on it (like a record player sort of, but much, much, much smaller). The time it takes to load things is partially affected by how long it takes for that head to reach it. By defragmenting you remove all of the junk that collects and move the useful stuff closer together so that it runs better.