RNG110 box - Guide works, can't access any channels

Hello, for about two weeks now our RNG110 cable box shows the cable channel guide, but when a channel is selected, the screen goes blank. I have rebooted the box and the modem, but the problem persists. We have Xfinity cable tv and internet, and the internet has been working fine.

I've tried the troubleshoot/reset on the xfinity webpage, but the troubleshooter says it can't find the cable box.

Please help, it's very frustrating paying for a service that we can't use.

thanks, Mike