Let's cover the basics then - is your live TV working ok? It sounds like it is, but that's not totally clear from your post.
I'm going to assume this is just a problem with your OnDemand services - I have a suspicion I may know what your issue is, but I won't assume anything so... What box do you have, is it a V6 or a TiVo? If you're not sure, check here
At what point during the process of finding & watching an OnDemand program, does this black screen happen? The more specific you can be, the more we may be able to help.
And are you using a 4K TV by any chance?
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