I cannot reset my Home Alarm - Veritas 8?

Last night my Alarm sounded when my light switch tripped in my living room. Both the internal (control panel) and external sirens were going. In a desperate attempt to stop them I removed the fuse which stopped the internal siren although the external one continued and eventually stopped of its own accord although I did get a visit from the police an hour later after one of my neighboirs called them! Although this was in some way reassuring I do not want to waste their time or irritate any of my neighbours!

I left the fuse out overnight and put it back in again this afternoon. As soon as I did so the internal siren started again and I could not get it to go off despite trying both the code and the reset button. Shortly after this the external siren started again and ran until it stopped automatically.

I do not want to get into a cycle of the alarm going off every time I attempt to sort it without reallly knowing how to go about it. The alarm was already installed when we purchased the house so other than my four digit code I do not have any other codes or installation information.