Car doors not locking on Vauxhall Corsa B?

The battery in my car has been flat for the last few weeks. I have just recharged it today and noticed that the central locking is not working, i can't lock the doors. Everything else is working fine.

I can put the key in the lock but i can't turn it, it's just really stiff. I can't lock it from the inside either, it's just the same.

Do you know what it could be?