Are there any blinking red lights on the front of your console?? I don't know if you have heard of the 3 red rings error on the xbox 360s. Its a very common problem for them. It usually starts with the console freezing or unable to read disc messages. I would check out a repair guide.
Here's one: http://kodyp.gamerbots.hop.clickbank.net
That should get you up and running in no time.
Jake
December 2009