how can I reset a veritas alarm system?

Can anyone help - we've just bought a house with a veritas alarm. Prior us getting the house the power had been turned off at the mains and now when we turn it on the alarm beeps all the time. We don't have a code (and can't get one - the house was a repossession). Is there anything we can do to sort this out and reset the alarm with our code without having to pay huge call out charges and all the rest, plus wait a week as no one can get to us till the end of next week?