Ldaquanno -- Were you able to get this fixed after troubleshooting?
I just recently had this problem. 3 hours on 3 separate chats with Comcast produced no results. I figured since they were seeing a signal going to the box, the problem must be after the box. So I bought a new piece of coax cable and reconnected from the box to my TV and voila, problem fixed. I believe Comcast provided that piece of coax cable with the box which was only about one year old. If you are using HDMI cable, try replacing it.
Got a new box, everything is connected but still says no signal. Don't know what else to do?
No signal usually means that the TV set is on the incorrect video input.
Check to see how your cable box is connected to the TV set.
If connected via RF-coaxial cable, the TV should be on channel 3 or 4.
If connected via HDMI be sure that HDMI is selected on your TV set (there may be an HDMI 2, HDMI 3, etc. input on your TV set, check them all).
If you have X1, be sure that you are connected to the HDMI output on the X1 cable box.
If you are connected via component cables (red, blue, green) be sure that your Component is selected as the input on your TV set
If your TV is connected via composite cables, (red, white and yellow) check that your TV is selected to Video or Game .
Also be sure that your cable box is turned on.