Schneider SVTV1451 Tuning Problem AV?

My TV/Video combi has now stopped displaying the picture on the AV channel. It has gone all fuzzy, but there is still a bit of sound and you can just make out the odd line etc when playing on my xbox through the scart socket. I have tried to tune the channel but it is locked and does not give the option to tune anymore, it just leapfrogs the option to the next one. I have tried tuning other channels to the right frequency to play my xbox all to no evail. Does anybody have a clue what is happening here, is it a problem within the tv?

Any help would be greatly appreciated.

Thanks, Ross