This happened to my daughter. She is 13 and does not understand Xbox very well. We tried throwing the Xbox against the wall, but this did not help.
What DID work is clearing the cache by pushing the power button, holding it in until the Xbox is off and you hear the drive making a faint buzzing sound... or just hold it for like 5-10 seconds after it turns off.
Restart, cross fingers, and try again.
I hope this helped.
p.s. I didn't really throw the first Xbox. I said that because I want to be cool but fail to time and time again.