Panasonic LCD was working fine. Now can't get picture or sound via any of the three HDMI ports. Cable and component input work fine. Tested cable box with another high def TV and it worked. Can HDMI ports be bad?

Yes, HDMI ports can be non-functional. Please post your TV's model number.

Is it just the cable box you have tried on the Panasonic?

Have you double-checked the resolution settings of the cable box?

I've only tried one cable box. I've used the component input through the cable and the cable from the wall to the TV (bypassing the cable box) and both worked. I haven't checked the resolution setting on the cable box.

I've only tried one cable box. I've used the component input through the cable and the cable from the wall to the tv (bypassing the cable box) and both worked. I haven't checked the resolution setting on the cable box.

Check the resolution settings. And post your TV's model number.

Do you have anything else with HDMI connections that you could test? Blu-ray player, upconvert DVD player, or even some laptops have HDMI out.