My xbox 360 wont show a picture but it has sound

check all your plugs and leads, make sure they are fully home and in the correct sockets

First thing to try, disconnect the AV cable and re connect.. Or if its the type with the switch that goes from HD to TV, flip it and see if it works

If none of that works, and your box is less than three years old, call Microsoft ( 1 800 MYXBOX ) and see what they suggest.

If your Xbox 360 does not have display you need to stop the heat getting to the chips. You can actually do this yourself as many have in this forum using the recommended Xbox 360 Repair guide.

Basically the guide will show you how to stop the heat build up with videos and household items, of course if you are in doubt send it in.

It has a preview video on the website.

Or of course you can send it in to have it fixed.

try a different input on your TV or replace the AV cables

just did one of those 1 hour ago
running great now
X clamp mod , it fixes so many problems.

Since your sound works, you know the xbox is booting properly.  Check two things: 1) try another television to make sure it's not the tv.  2) try another cable(from a friend?) to see if the cable is bad.
**Also, if the video settings were saved on an unsupported setting, it could cause the screen to not show video.  If you try these 2 things and you think someone might have saved bad settings, I recall a button combination you can use to reset certain things, and I try to help if it comes to that.

It's possible that your Xbox is sending out a picture that's higher resolution than your TV can display. Try reducing the resolution of the Xbox video output.

try using a different input on the tv or a different tv. make sure that you used a totally different av cable. if this all fails then you have an internal hardware failure

I would try some of these troubleshooting steps;

1. Make sure that the AV cables are 100% secure.
2. Try an new AV cable.
3. Try your console on a different TV.
4. Call xbox customer support at 18004MYXBOX

Check your AV cable if your tv is HD push the tab to HD if not set it to normal tv this should help you out. If that doesnt work i would try to borrow someones AV cable and try that.