How can I fix the picture on Grundig GU108047IV 47" LCD TV?

I've inherited it from a friend. When you switch it on at the wall (i.e. when it is cold), the picture is fine. Then after about 1 minute, the picture starts to break up then freezes (sound is fine) and then you can't watch it at all. It seems like it only works when its cold.

I don't know anything about TVs but I wonder if its something like a fan thats broken inside? And then maybe it gets too hot and the picture goes? I know its not the aerial as it does this elsewhere and the TVs that we have already work okay in the same aerial ports.

Do you have any ideas?

Louise
March 2009