I am assuming that you have your pin code ? please confirm..
On this version of the Beosound 9000 the pin code can be de-activated, if it was previously de-activated, i.e. if you turned the power off for a while, on switching it on again, it did NOT ask for a pin code, but due to some problem it has been re-activated, then you will need the pin code to put it back to its previous state.
So, what happen just prior to the problem occuring ?