Why is the filing cabinet not unlocking with the key?

There could be several reasons why the filing cabinet is not unlocking with the key. It could be that the key is damaged or worn out, the lock is jammed or broken, or the key is not the correct one for the lock. It is also possible that there is an issue with the alignment of the key and the lock mechanism. It may be helpful to try using a spare key or contact a locksmith for assistance.