my xbox 360 has stopped working all of a sudden

hey, i would just like to know why my Xbox 360 all of a sudden stopped. this Xbox has been kept in our cabinet all the time, so could't be water damage/hard drive failure. not much has been happening to it leading up to the event. so, when i turned it
on this morning, the green light in the middle turned on for a second then turned off and did nothing. my friend's DVD is stuck in there, and he want's it back. do you know what might have happend? feel free to ask questions about it, just don't know what
type it is. FYI (for your information) it is a thick black Xbox.

:)