This may be old news, but I can't seem to find the correct search terms to find it.
I leave my WMC running all the time. Normally I just tap a remote button and the picture comes up. Some time ago I had issues with powering up my TV and having no picture from WMC. I hunted around the web and found others with the same issue. They claimed it was an HHDMI handshake issue between MC and the TV. For whatever reason the problem seemed to clear itself up. Now it has returned. I have to pull the HDMI from the TV and put it back in. This seems to reset things and I have a picture.
Is there a fix to this problem? I had the same problem with a satellite STB a while back that seemed to be fixed when I changed the HDMI cable. Can that be the cause?