tfclark,
It may be as simple as the box itself. In some cases, the resolution from the box menu system is a different resolution than the signal that's being transmitted. So it would look like this:
One signal:
1080i signal - television show
480p signal - menu resolution
Since the signal can't carry both signals at the same time, one signal may conflict with the other. It sounds like one of those "Gee, why didn't they think about this before" issues, but strangely enough, that sounds like the cause of your symptom.
Your best bet is to see if the content provider (cable/sat company) can assist you in changing the settings for your TV guide widget so that an equal resolution is sent.
I'm not positive, but I would guess with some certainty that this is the cause of your problem. If this is the ONLY application where this causes your picture to turn black, then I'd say it's a good guess of where to isolate the problem.
Also, turning off just the cable box should bring up the picture. Usually the box's HDCP (Copy Protection technology) will cause the picture not to be sent. Restarting the box starts a new connection, and also points to the box being the issue.
Keep me posted.
--HDTech
I have a LN46A850 connected to a Verizon FIOS Motorola HD QIP 71001 HD cable box using a HDMI port. When changing channels or using the FIOS TV Guide to change channels, video is lost on the TV, and the screen will go black, audio is still present. There is no loss of signal message displayed. The only way to get video back, is to turn off both the cable box and TV. The TV is about two months old.

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