why is my computer pinwheeling/freezing every two minutes?

hello,

I have been having issues with my macbook pro for a couple months, now. When it started, I would just close my computer monitor, and open it back up a few minutes later, most of the time this would kick it back into gear, but would pinwheel all over again in a few minutes. Incredibly frustrating. It does it in every program, even if there is just one program running, from itunes to iphoto, or even just searching my mac.

Once I had to force shut down my macbook by holding in the start button. I waited another half hour or so to start it up, upon which it was flashing a question mark over a folder on grey screen. I had to upload from startup disk everything all over again, and the pinwheeling has just gotten worse, since. My local apple store is complete crap and they did not fix the problem both times I went in, and had to speak with applecare over the phone to have a new startup disk sent to me, since I had moved and simple items like that had not yet made the move with me. Anyone else have a similar problem or suggestions to fix this. I'm afraid every day that i'm going to loose my computer.