Back when I was a gamer I used to shut down a few computer processes so that I could run the games of the day a little faster.
There are free "accelerators" available for download that automatically shuts off services and processes to give your machine a speed boost. These accelerators, then, according to theory, restart the services and processes when you're done gaming.
I've never tried them. Personally, I'd recommend you look a little deeper. It could be malware. There are free online checkers to supplement your own. Maybe one or more of your drivers aren't quite right and you have a big memory leak someplace. It might even be some bizarro problem with your HD (or at least your swap file, though that seems less likely). You might also have a faulty stick of RAM.
Then you might give PC tune up software a try. I like Ccleaner and Glary utilities. I also on occasion use Puran utilities. These are all free, and are intended to clean up and fine tune a windows install. All of them should be used with caution and care. Though they can really help, they do have the potential to hose your machine.
Having said that, I've used Ccleaner and Glary for years, and Puran for months without incident.
Check a reputable freeware site, such as Snapfiles or Major Geeks for the aforementioned software.
Final words: if you're feeling insecure about most of the above solutions, it might be time to make some fudge.
Have your friend over and have him troubleshoot.