Hi Mr Ball,

Thanks for the question, the black sliding lever on the front should move quite easily if the correct numbers are in place. As should the lever inside to change the numbers. if they are not moving either the correct numbers to unlock the box have not been put in place. (numbers should be all in center of the dial not higher or lower than each other) if this is correct it would imply the lock has been jammed or forced in some way. you could try wd40 or similar to see if that helps. release the mechanism.

Hope this helps.