Problem with COX Contour receiver

Our system has been problem free for several years, then a couple days ago I realized I could not get a signal from the main Contour receiver and the local TV. All of the other boxes (we have 3 others) are working fine, but the main box is not sending signal to the TV that's connected via HDMI. When I unplug it for a couple minutes and plug it back in it tries to start up and the TV displays the "welcome" screen for several minutes, and then the "connecting to your experience" screen followed by a black screen. With no response to any of the remote-control commands and no way to exit out, it's just a frozen black screen. The box still sends the cable signal on to our other three boxes, but I cannot figure out why we lost the signal at the TV that plugs into the Contour receiver. Thanks in advance, any and all suggestions are welcomed.