craigp,

Welcome to the saloon! When I have run into issues in my HT I start with the easiest things to fix. You may have already checked, but make sure all the cables are well seated; a loose cable can cause intermitent problems. It looks like your video issues occur when you use your Comcast cable. Are you using a new cable box or changed the box's setup? You may want to do a hard reset of the cable box. If so, you may want to revisit the setup/reset with Comcast technical support.

I have run into a similar problem with the surround speaker/tv speakers in a family member's system. He has a Panasonic plasma TV with HDMI inputs. The HDMI connection provides audio to the TV even though it is preferred to have the sound from the AV receiver. If you have connected directly from the Comcast box to the TV with HDMI that could be the problem.

There a lot of very knowledgable folks in the Saloon. With a little more detail on how you have connected your system I'm sure the Gunslingers can figure out why you system is misbehaving.