Overvoltage possible? Do you have a surge protection? Try to reset with disconnection all cables and interconnects.
Br A.
BS 1, BeoCom 2, 2x LC 2, Form 2, BS 2, BS 3, 2x Beo 4, BS 5, BM 5, BL 5,Beo 6, BS 6, 2x A8, BV 8-40, BL 8000, 3x A9 Keyring, Serenata, BeoTime, BeoTalk 400