MacBook keeps freezing, some keys not working. What might it be?

When I turn my Macbook on, it turns on fine, I've had a few problems with it in the past but took it to Apple when it was still under guarntee and now it's broke again. First the CD drive keeps sticking and doesn't work very often. Also, when I turn it on it loads fine and all the startup programs load but the mouse and the keyboard are just frozen and it needs to be shut down and restarted quite a number of times before it'll work again. Also the C key doesn't work and sometimes the keys around it dont work, so when it does load up and isn't frozen, often it'll work for a few moments and then freezes or if the C key or others that don't work around it are clicked a few times the whole thing freezes up. The trackpad just stops working the mouse freezes, I can't click or type but the screen is still running so if I have MSN up it'll still receive messages and such. Please can you help on what might be the problem or what I should try?

Thanks