are you running your audio through a different source as your video (5.1 system, etc.?)
Did you recently change monitors? If so your resolution may be off.
Sometimes there is a switch on the av cable where it plugs into the console that switches between HD and standard, and can be accidentally bumped.
Lastly if you are using Hdmi, the cables frequently go bad from stress (bending) the one im using now has to be wiggled sometimes before it will put out video, yet the audio will still be working.
no, i was usin same monitor ,then tried another to see if it was the monitor. when that didnt work, i bought new cables, and that didnt help..and no switch on the cable..so is there something else im missing? ty