Have you got the new software? If you check series links and it says 'series link +' then you have. In which case take out the viewing card cos it's causing problems and isn't reqd anymore. Then try home-thumbs down-thumbs up-play play. You'll hear a beep and the screen should Ho blank for a minute. See if that does it. If not it'll be another engineers visit I'm afraid.
Ps have you tried a new (but cheapo HDMI cable? I found the expensive one I had caused no end of problems. Bought a new one for a fiver and hey presto fixed!!)