ford mondeo 2001 central locking problems?

!hi paul pls help!! last year the key fob stopped working for remote opening of doors so i just opened doors manually. After very cold weather, doors would suddenly lock while i was in the car. Not too bad but a few months later the key wouldnt open the doors manually key looked worn down. Took car to ford and they cut another key (not fob key) and had no problems opening door. Now after cold weather again after unlocking door manually, as soon as you open any door to get in the horn alarm and flashers go off and if you try to open door even after 30minute journey the alarm goes off again. Tried reprogramming old key fob to see if that works,but nothing happens. So fed up now i wont use car and afraid of bill from ford if i bring it in. Any other ideas? i am not handy so wasnt able to open fuses to check