My xbox 360 elite had

Question

My xbox 360 elite had recently stopped dislplaying the video on the TV. The sound however is fine and can still be heard. I've had the unit for nearly a year now and this only started happening the other week. I was round a friend's house and initialy when the TV began to turn to greenish i thought it was in fact the TV. However after a very thorough inspection me and my friend both came to the conclusion that it was not the TV or the cables connecting my xbox to the TV. We found this out by simply pluggin his xbox into the setup for mine and it worked perfectly. Therefore i am 100% certain that this problem lies with the untit itself. As i don't know anything about electronics and don't want to void my warranty i was wondering what you could suggest to help?