alarm not working after turning power off

[skyblue]

My burglar alarm has ceased to function after having the power off, it is an ADE Optima Compact. After switching the power back on every LED on the control panel is lit but there is no response from the keypad. I've looked through the manual at

I can't find any reference to this situation. Could it be a flat battery? Any ideas? TIA Skyblue

[Sparks]

When you disconnected it from the mains, did the internal battery take over powering the system?

Is this battery (that is presumably flat) still connected?

The installation manual states the battery should be connected before the mains, but assumes the battery has some charge.