How can I fix my central locking on Vauxhall Zafira ('54 plate)?

My fob hasn't worked for a couple of years, so I've been locking/unlocking manually with key. This morning it unlocked, but then I couldn't lock it when I got to work. Also I can't lock it with any of the door "buttons" as they won't depress! Have tried locking from the outside using the boot lock, but the key won't turn in any of the locks.