Accenta Optima G3 - Steady Attack light. Can't reset?

I have an Optima Accenta G3. After the panic button was pressed recently (my young daughter did it!) I turned off the alarm by keying in the code. Now the attack light is steadily on. All other lights are off (except power and day lights) and the reset button has no effect. Rekeying the code does not change anything (no beeping sound either from keypad).

Any ideas on how to reset it?

Thanks
Jesmond