First, I'll say double check you're on the HD channel. Some cable companies have both SD and HD version of the channel. For instance, until recently, my cable provider had channel 5 as regular FOX and 705 as FOX HD.

Next possibility is a wiring issue. With the old TVs, you could just plug a coaxial cable (that little plug with the small needle on the end) into your TV or cable box and that'd be it. With HD though, you need either:

* component cables (which are colored red, blue, and green, with a red and a white audio cable), or

*an HDMI cable, which is a simply black wire that looks like a plain USB computer wire that you'd plug into the side of a laptop.

So, double check the back of your cable box, and make sure you have one of those two things, and not the old cable that SD TVs used. When I did tech support, one of the leading causes of this problem was that the cable box was wired up using the old type of cable (which can't carry the high resolution of HD).

If this is the issue, you'll have to hit the input/source button on your remote once you've plugged in the correct wires. Set the input to HDMI if you used an HDMI cable, or "component" if you used the red-blue-green wires.

If none of THAT works, then call up your cable company; it's likely a configuration issue with either the TV or the cable box.