Is it cold where your laptop lives?
:) no no just kidding, Hard to determine what the issue is without knowing is this a Mac, IBM, where is it freezing, on boot up, when you try to run a program etc. You can try to follow The10DollarMark's suggestions, but if it is freezing, you might have a hard time doing that, I could suggest a free virus detect n protect, but not sure that will lead you down the right path, with out more info.
Certainly if somethinig is going wrong with the laptop, over heating, hard drive issues, etc
If you can provide a little more info.. does this randomly happen at different times, or only when you load a web page, or a program, on boot up. Is this XP/Vista/New Windows, etc..