Sounds like an ADE panel
Does it have Optima, G3, Accenta or Concept written on it? Is the RKP rubber keys or membrane?
The RKP will lock-out on tamper, and only return to day when the fault is cleared.
Try the following: any panic buttons, rkp's and covers for PIR's - have any decorators been?
If this fails to find the problem, remove the panel cover and insert a link in the tamper terminals, this will remove the fault, then the panel can be returned to day mode.
To walk test the system depending on which panel it is, you may just need the user code or the engineer code. If you need the engineer code, try 9999. If this fails to work, you will need to reset the NVM. This you do by powering down mains and battery then shorting out two terminals on the PCB. The terminal numbers depend on which panel it is.
If you're really stuck, e-mail me and I can send you what details you need. I have instructions for 99% of ADE's panels.