remote central locking doesnt work on my astra?

Hi, I have an astra convertible MK4, the remote central locking has stopped working. I have tried all your tips on the site and it still doesn't work? I have tried another key, replaced batteries. The key works if I put it in drivers door, when I lock it its fine using the key but when I unlock it sets the alarm off? I have tried disconnecting the main car battery and reconnecting later, still no different, could it be a fuse? really need some help as don't want to take to garage! The roof, radio everything else works, boot etc.