How can I stop my laptop freezing?

Hi, I have a hp laptop that is a couple of years old. I don't know anything really about model or processor. Yesterday it started to freeze after a few minutes, so much so I had to turn it off. Then it wouldn't turn back on, I could hear the fan going then it would stop and nothing would happen. Today it worked fine in morning then same thing happened again the evening. I managed to get it working again long enough to run a windows registry clean up which identified And repaired 300 odd errors. However, it has now done it again turned on, finally after 3rd attempt, then froze on main screen. Now won't turn on again. Any ideas???