Please. how to mend, or reset or restart Texecom Veritas, (8, I think)?

After electricity cuts yesterday the strobe is flashing outside, the code number is ineffective altogether, does nothing now, and the keypad keys just give the same dull sound when pressed, nothing else.
Of four detectors inside one is persisting in alarming at every slight movement in the hall, causing ten or so beeps, then subsiding, then again beeping with any movement at all. The other three remain normal, quiet, causing no alarm or beeps; their function may be correct, while that in the hall is wrong, defective.
The code number alters this not at all, has become ineffective, and fails to reset, to stop the noise inside or the strobe outside. I have tried everything I can, for hours, at wits end; please help, please advise. Faithfuly, Timothy