Have you checked your drivers? Is the TV 720p or 1080p ready? If the TV is neither of these then you will not be able to display anything. maybe you can supply more details like the model of the tv and your computer specs
How are you connecting your pc to your TV? I connected my pc to my HDTV and could only get a max resolution of 1024 x 768 with a s-video cable, i then connected it using a VGA cable and could get the max resolution which was way up there in the 2000's i forget what it was forsure.