XI TV Box Not Working

I bought a new HDTV to replace an old standard (non HD) TV.  The XI TV box was working just before I switch out the TV's. I unplugged the box and cable to the wall outlet so that I could reconnect it to my new TV. I followed the Xfinity installation video to make sure I connected the HDMI cable & coaxial cable properly.  When I plugged the box back in the light indicator is not on. I checked the cables to make sure they are tight. I also completed a remote troubleshoot/diagnostic and it says that it is connected. My new TV keeps saying there is no signal and cannot complete uploading channels. Not sure what to do next?. Any suggestions would be greatly appreciated.