Disco 2 Alarm Issue

I have a Discovery 2 on a Y plate. I have been away and on return home the battery way almost flat on the Disco. The doors would not unlock with the fob so I Unlocked with the key, Lifted the Bonnet and charged the battery. After about a 3 hr charge of the disco the Key fob will now lock and unlock the car. But the alarm light keeps rapidly flashing and when I go to start the car the alarm goes off. I would have thought because I have now locked and unlocked with the fob all should be well. Do I have to leave it a while. I am still charging the battery on the Disco to get plenty of charge in it.
Any advice appreciated

Dennis

you say you have it on charge, is the bonnet still open on it lach? Cuz if so alarm might not be resetting. . Shut all doors and bonnet. Lock with fob and then watch the led light to set . Then try again

Turn ignition o II and leave it so 5 minutes then unlo ck with the fob and try