fiat ducato 2002 won't start?

just before christmas i tried to start my van in the freezing wheather and it would't start up so i kept on trieing and the battery went flat, then i charged my battery up again and i noticed a red light/symbol on my dashboard of a car with a padlock through it and since then it wont even turn over. my starter motor makes a sound for about 3 second when i first try then nothing. what can be wrong with it??