Connectivity Problem...Panny 58 60u

was looking for a tech support section but couldn't find it so am posting here...

just got a panny 58 inch 60u set and i can't seem to get an hd signal from my comcast dvr box to the set. however when i have coax out to the panny i get the signal fine. i've tried two different brand new hdmi cables, both hdmi 1 and 2 inputs on the set and have rebooted the dvr box. i get a totally blank screen, no signal at all getting from the box to the set. i called panny and they said it had to be the box, and i called comcast and they don't know what's going on. for now i'm watching the set using coax but that's obviously not what this set is capable of. very strange, it should be straightforward hdmi from box to set but it won't work. i think i may go in to comcast to exchange the box, but any other ideas would be appreciated. thanks!!

very good suggestion, just went through that exact scenario with the comcast support person. in the menus there is supposed to be some sort of hdmi option which on my box doesn't exist. comcast is coming out tomorrow with another box, hopefully that's the issue....thanks!

the box is a 6412 III...comcast and i have no idea why it's not working, but it's not. tomorrow they are coming out with a new box, then we'll see.

comcast came out and replaced the box today....it was defective, the guy said about 50% of them aren't right so if any of you using this box aren't happy with your picture you might want to make sure you are getting the right signal...anyway, my wife says the picture looks great (it wasn't bad on analog) so i can't wait to get home to check it out!!