Is it opening when you press No Sale? If your answer is no: Do you have permission to open the cash drawer for a No Sale. This is a user authroization in Office under Employees - Job Types - choose the type - Then choose 'No Sale'
Is it opening when you press Cash sale If your answer is no: Was it opening before? If yes, then continue, if not then to go Office - (main toolbar) - System - Tender Types and make sure that the cash payment option has 'Is Cash' checked.
Your computer should be connected to the cash drawer. Identify how using these points as a reference: