Just installed theV6 and within a few minutes exactly the same problem.
All was fine, but after 10 minutes setting up all my series links I went back to tv and ... no picture but sound and all menus were fine.
Rang up Virgin and they reset the box and no difference.
Re-powered everything and no difference.
Then the V6 suddenly decided to reset itself and the picture came back.
Not a good start.
I also have a Sony Bravia TV which has been fine for 3 years with Tivo, Bluray, PS3, Humax , Apple TV and a Sony home cinema receiver.
I would have thought if my TV can cope with 1080p from a bluray then 1080i from a V6 would have been a piece of cake.
So I wonder if Virgin will come back and say it's my TV that's at fault given the only thing it's had problem with is a V6?