reseting a veritas alarm?

We do not use our alarm, but do have the code. The other day I was out and we had a power cut, when I came into the house the alarm went off, I tried entering the code and reseting it, but this did not stop the alarm. I phoned a local electrician who had recently done some work for us and he told me to disconnect the battery and take out the fuse and to get a new battery and reconnect it. I got a new battery and reconnected it and perlaced the fuse. This did silence the alarm, but the outside alarm light keeps flashing and when you walk by the sensor near the front door a beeping noise starts for about 7 seconds and then stops. I have tried re-entering the code, but this does not stop the light or bleeping. When we have had power cuts in the past the alarm has always reset when the code has been entered. Can anyone help?
Thanks