I have a Panasonic 42 inch HD TV. About 4 months old. When I want an HD channel it comes up and says wait and it takes 5-10 minutes before it comes in. Then when it starts, it's all juddery and off kilter. Little boxes of color that shift around. The screen goes black.

Where did you buy it, should be under warranty. Which exact model did you buy?

Also, what do you have connected to the TV? How is it connected? Do you have this problem with any other HD source like a Blu-ray player?

I'm willing to bet you have a cable or satellite box, and that it is set to display the native resolution of the channel. If you have access to the resolution settings, see if you can set it to only output in HD resolution. It sounds like the box might be having issues either switching output resolutions, or is having handshaking problems because of the change in output resolution. Basically, when you change channels, your box has to "disconnect" and "reconnect" from the TV when it goes from a standard channel (480i resolution) to an HD channel (720p/1080i).