Door locking and alarm fault

I have just bought a 97 Ford Escort LX 1.8TD with 112000 miles with central locking and deadbolts and factory alarm I locked and deadbolted the car yesterday and the heated rear screen light came on, it is only on when the car is locked, I tried to open the car this morning using the drivers door and all the doors except the drivers door unlocked, tried the passenger door but the drivers door still refused to open. I locked the car using the drivers door then unlocked the car using the passenger door and the drivers door could be opened, this has occured twice today, the alarm is supposed to sound if the bonnet or boot (hatchback) this does not occur, I unlocked the car yesterday and opened the bonnet the alarm went off, I also opened the boot later with the car unlocked and the alarm went off, the only way to stop the alarm was to turn the key to the unlock position in the passenger door as the drivers door did nothing to stop it can you help please?