PA stands for " personal attack ", these are usually fitted in a bedroom, looks like a little square box with a red push switch on top of it.
The PA is wired directly into your alarm panel, so either the PA unit is faulty or the wiring is the problem.Have you had any carpets fitted recently,or any work done that could have damaged the wiring?.
Find the PA switch and inspect for damage, or it may have been pushed accidentally and needs resetting.
e manno
August 2012