In case of desperation, try this:
I had to unplug my TV and cable to move it as I was putting my living room back in order. Of course, I couldn't get the cable back, rebooted 3 or 4 times, and I knew there was some combination of things I had to do in the correct order to restore service. Well, everything I tried failed...and out of nothing left to try, I pulled out the various cables connecting things to the TV and cable box and plugged them back in -- lo and behold that worked. Don't know why, but it did.