Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Listen carefully, when entering the code to unlock: Do you hear a 'click' when you press ENTER or complete the code?
If not, the latch is 'dead' and probably the batteries too.
If so, the latch is stuck or jammed... and try rattling it some, to see if that jostles it loose.
Let me know and I will advise you further.