Tv 360 - picture freezes then screen goes black

We changed to tv 360 a few months ago. All seemed well until this week. We are now getting instances of the picture freezing then the screen goes black! If I channel up, or down, the picture on adjacent channels seems fine, but when I go back to the affected channel I get the black screen. To get round this I have found that if, when on the affected channel, I press OK to bring up Program Info, then press OK again to bring up the "Watch, Record, Episodes etc ..." options, then select Watch, then select Watch Live then the picture returns to normal and I'm able to resume watching my program. This problem is NOT restricted to a particular channel. It occurs on different channels at different times. 

I'd be really grateful if someone has a remedy for this because it's extremely irritating having to go through my "reset" procedure to solve something that wasn't a problem until we got tv 360!