We turn the tv and xbox on but there is no picture. We can hear the xbox power up and the tv works otherwise, but no visual for games.

Your hanna chip (output) is fried......sorry

If the console turns on (you hear fans running and the ring of light is lit), possible issues may be:
1. TV is not on the correct input setting.
2. Graphics card failure (If under warranty, you should be able to send the console to Xbox for refurbishing).
3. Other hardware/software failure.

If the console doesn't turn on (No fans or lights), check the following:
1. Is the power brick plugged into a wall socket?
2. Is the Xbox plugged into the power brick?
3. Is the power brick LED lit? (If you answer no to this, the power brick is likely the problem.)

I need more info, are you runnig High Definition? Are your cables connected properly? Is your TV working properly?
If you're running on a Standard Definition TV check the back of the Xbox and see if the video switcher says SD.

Does it get the three red lights around the power button if so go to the xbox website and they will repair it for free

make sure the hd switch is not turned on on the video cable that connects to the xbox, it is a small black switch

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.

I guess when I moved the xbox i hit the swith for the hd and regular tv. It's on the back of the xbox next to the power cord plug in. I could hear sound but i couldnt see the screen. When I swithched it to TV the picture came on.

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

my screen is green.  i can hear audio but no picture.