JC: All of a sudden the stand-by light on the 9000 started flashing and a strange clicking in the unit, as though switching on and off. The 9000 will not switch on and the 3500 will not recognise any source from it.
Jonnie,
Based on your description of the problem I think it is unlikely that the B&O hospital will find a problem when they test your unit particularly as you have already disconnected the BS9000 and it apparently then worked.
Generally speaking I would agree with other contributors that the Masterlink would be the first area to check.
An open circuit/high resistance ground connection within the Masterlink cable would often cause this type of problem.
At the time of the problem starting was there ANY other electrical equipment plugged into the same mains supply (same power ring) ?
JC: I know the problem is not the TV as I have a second TV and as soon as the 9000 is plugged into it the flashing and clicking starts immediately.
When you plugged in the second TV in, did you use the SAME masterlink cable or a different one ?