Hi - I am having the same problem with my 97 Disco.
It was running great and I pulled into my driveway and turned off the car. When I opend the drivers door to get out the alarm went off and locked the engine. . .in essence it immoilized the ignition as if I was steaing the car. I tried everything- new key fob battery,disconnected the tumblers in the drivers door and using a universal code 1-5-1-5 locked unlock code . That worked a few times to start the car but was short lived. It was going off by itself in the middle of the night so I had to disconnect the battery. Now I just cannot get it to start at all. It tries to crank over but no luck. (And yes I connected the battery back and ensured it was charged. . ) Thanks for any help!! DD