No Image on Screen. Hello! I have a Sharp LCD TV: 20AV6U. I bought this new from Best Buy 13

Question

Hello! I have a Sharp LCD TV: 20AV6U. I bought this new from Best Buy 13 months ago. (I cannot find the User's Manual). This tv is connected to a Comcast Cable box and also a DVD player. I have had no troubles whatsoever with any of these components. I recently went out of town; turned the tv off; came back home, turned the tv on, and there is no image whatsoever on the screen--just a black television screen. The audio works perfectly. The channel display is shown on the screen; the comcast digital information for each channel is displayed as well. But there is no other image on the screen. Any help you can offer will be greatly appreciated.