Veritas 8 reset fault, help please!?

Hi. We've had a Veritas 8 fitted since 2002 and used it without problem for the first 3 years. Circumstances changed and we haven't used the alarm system since. Recently i needed to take the lighting fuse out of the fuse box which has set the alarm off. When i tried to reset the alarm there are certain keys on the key pad that don't seem to respond. ie when i press '1' you here a bleep noise, however when i press '2' there is no bleep noise. The same applies to the 'reset' button, no bleep. I know the code yet it won't allow the input to be made. Is this some type of installer lockout? Can anyone help with this issue? Thank you so much.