I've had the same problem. Over the last 2 months since I've gotten comcast service I've had a tech out because I couldn't get anything on my main TV (where the DVR is). After the first visit, I noticed the box had been switched from HDMI1 to HDMI2 (same box stayed). I didn't think much of it at the time. I just kept it there. Then it happened again. Last night the tech came out and moved the box to HDMI3 and it worked. I tried to communicated what I thought was happening and that my ports are getting damaged by the box so they finally replaced the box but now I'm sure those ports no longer work. I'm going to test them tonight with my PC. Not sure what path to take if those ports are damaged.
Personal information and soliciting.