The cash drawer is usually connected to the RJ12 connection at the back of the receipt printer. 
This means that if the receipt printer has a problem, the cash drawer will also stop working. 

Then the setting below is set to "Printer1".

Solution

Start by checking that the receipt printer is turned on and connected. Then check the cash drawer settings.

This must be set to Printer1.

If the cash register drawer is not set to this, adjust this, save and try to open the drawer again.