My key also stopped working. I had to open the door manually, which activated the alarm, but the car started and all was fine. When I returned home, I tried the second key and since then I am using that one. After reading the stories about strange things happening with the batteries, I have not tried to remove the battery of the good working key. I have not even replaced the bad battery key. I just wait for both keys to stop working before trying anything.
As I said before, there seem to be no special fuse for the locks, at least in my manual. But if you think that this is the problem, you could remove all of them one by one and find out whether a fuse that does many tasks has gone.
As the central locking works with the key, I think the problem is the key battery and programming. I am not sure whether a key loses its programming if it runs out of battery. I could end up in this problem at some point. If that is the case, then by removing the battery from the good key, you may have lost its programming. If that theory is right, you then have no keys programmed. But if you think about it, the programming is more likely to be about the immobiliser and not the remote locking. And I do not think that the receiver is not working as well but I am not sure what you have to do to fix the keys.