My questions are:
1. It sounds like you have just pulled this out of storage. Had it failed this way before the storage ? Did you see when it failed this way ??
2. Do you have a lead to connect to the RGB port such as RGB to Scart ?
3. What sort of screen are you using ? Are you sure it works ?
Another idea, does anybody know if an A500 external rf modulator module works on the back of an A1200 ? If so it may give you another chance if the internal RF is fried.
Good luck :-)