My computer runs fine but freezes often?

So I've had this problem starting a few days ago. My computer will start up fine and will run normally for maybe 5-10 minutes but then it decides to randomly just freeze up. I can still move the mouse cursor around on the screen but no programs respond, not even when I hit Ctrl+Alt+Delete. The only way to get out of this is to force my computer into shutdown. I was able to run safe mode for a while but that eventually froze up too. I have tried multiple solutions in the "Event Viewer" and I was defraging the hard drive but it crashed. Nothing I have done so far has seemed to help, currently I am about to take the computer and clean off the heat sink and fan and apply some new Articsilver. If anyone knows a solution to this problem your help would be greatly appreciated, or if you can redirect me to another site with the solution. Please do not give me a link to one of those free registry cleaners or other programs, I know not to use those already and I will not even touch them.