No picture only sound/audio on HD channels?

What is wrong with me Comcast HD box & why do I get sound but my picture on all the HD channels?

• The regular channels work,I get picture and sound on them channels,but when I turn it on a HD channel a blue light comes on the front of my box and I can hear the sound on the HD channel,but there is no picture,only a blank screen.What do I need to do? Additional Info- I have a 32 inch Advanced serious LCD HDTV(it has 4 HDMI ports and the port I use is port number 3 and there is a coaxial cable running from my room wall to my HD box and I also use an HDMI cable.

• Answer:

  I never had that problem, but I would try a differ port, then different cable, unplug the box, then try again, try turning the box off and leaving the tv on, then press menu on the Comcast remote and try messing with the settings it brings up, and if that dont work call Comcast and ask them to send a tap for the HD to your box, if that dont work, go to a comcast store and switch out the box for a new one.