i havent really used the hdmi inputs on my tv in awhile. i had an xbox that only had the colored chords. but i just got a new xbox and cable. the picture looks great but there is no sound from neither my cable box or my xbox. but when i plug the old colored chords in the sound works fine. I also have my desktop plugged into my tv as a monitor. and the sound works on that too. is something wrong wtih the hdmi input?
Do you have anything else with an HDMI connection you can plug into the TV to see if you can get sound from that device? Is your desktop connected to TV by HDMI? If not, and if your PC has an HDMI out put, try connecting it to the TV by HDMI and see if you get sound through the TV speakers. If yes, then the Xbox is the issue. If no, try different HDMI inputs on TV.