Please Help, Macbook will not start

Ok, so I was playing WoW and messing with iTunes, as well as watching some youtube videos, when suddenly my macbook (2.26ghz black 2007 model I believe) started being SUPER slow. It would work well for 5 seconds, then freeze for 2min...

I closed the macbook just to see if anything happened, and then it wouldn't start up.

Now it's at the Apple Logo (Grey Screen) with the loading sign unable to start up.

Once or twice after around 5-10min, it has gotten to the login page, and I typed in my password correctly, and it started loading the background, but then froze, took me to the login screen all over again.

ANY HELP WOULD BE MUCH APPRECIATED!

~Thanks in advance!