I use both my coax and hdmi ports. On occasion when we get a reboot it stops working. Every time I call Comcast they are never helpful. It takes me a week and 10 repeated calls to get someone who knows what to do and sometimes never. Finally I have decided to post this for my reference and someone else’s. First off I have a older projection tv that accepts 1080i and not 1080p which this article may help others with the same issue. Even the techs who bring the boxes out don’t know how to hook this thing up with the hdmi port. So what I have found that happens is the x1 box when powered on will search for the best signal. Usually putting 1080p over the coax. Therefore turning off my hdmi port. Since I have an older tv the hdmi port is not easily detected when you plug in the hdmi port. This could very well be happening to you. You will have to plug the hdmi port into a device that communicates back to the x1 box and tells it I need to be on a particular resolution. Sometimes this requires taking the box to another room. Now keep in mind. It will automatically choose the best resolution for the hdmi port. In my case I got the coax working, then plugged a device in that told the box to turn the hdmi port to 420 Sd. Now that I have booted the box and have both the hdmi and coax operating at 420 sd the box is now able to connect back up to the old projection tv displaying a zoomed in like picture at 420 sd. Now I can go to into the x1 settings then devices then video display options and change the resolution up to 1080i. The tv flickers some and when it gives the option to accept the changes, say yes and it should stick. You can use this to resolve an issue trying to get the hdmi port set on a resolution that the tv can not auto detect when just plugging in. So keep in mind hook the hdmi to another device. Get the resolution down. Connect back to the device you trying to get work. Then bump up the resolution to what is compatible. This case can be close and I was just sharing because I go through this issue every once to twice a year and for some reason customer service does not know how to resolve. And my memory is horrible. I finally wrote it on my box. I called this last time and the guy told me I had the tv on the wrong input closed my case without my consent. My hand is on my forehead.