Hi Dave,
I am having a similar problem after a power cut. I Isolated power on mine and took the cover off and the engineers (don't you just luv them) had left all the install / service guides inside. Tried an NVRAM reset (to no avail) and have just attempted a fresh install as per the manual (also to no avail). Turns out a guy at work is an ex alarm guy and between us we believe that an 8 - 9 hours power cut will have drained an 8 year old battery dead. He told me that they used to replace them every 5 years and that recommended maximum is 7 years. If you are still looking for answers, I can scan and email you the manuals that I have and one I found online. Also, I have just found suppliers of new batteries (appx £10) and control units (£37).
Rgds,
Keith (07986 272 106)
March 2009