The main mechanism used to open the drawer is a lever that can be controlled with both the back switch and the key. The most common reason this mechanism fails for the key is because the lever in the back is bent. To troubleshoot, first remove the drawer from the cash register and turn it upside down. If you use the key, you will notice that a lever that sticks out the back moves. With the drawer upside down, bend the portion of the lever that sticks out downward (towards the top of the drawer). Also make sure that it is perpendicular to the edge of the drawer. After manipulation, place the drawer back into the register and the key should be functioning.