that problem could be the result of a million things.
I would update all your drivers. download all your hardware manufacturer's BIOS flashes, and ROM flashes, etc.. All the windows updates.
Secondly, check your antivirus to make sure it's up to date. If you don't have an AV running, buy one. Don't go for the free stuff. Pay money, and get one that works.
Thirdly, hardware, which is somewhat unlikely. If you're CPU fan (or chassis fan) is burned up, your PC will act erraticly. If your hard drive's platters are going bad, the drive will spend a lot of time moving data off of bad sectors to new sectors. Run defrag and scandisk.
Lastly, clear all the junk off that you don't need. (before you run Scan disk or defrag) Any temp folders, including internet files, get rid of it. Uninstall unnecessary applications.
I hope that helps.