Sorry to hear your cash drawer isn't opening. Your drawer is actually connected to your receipt printer, and often problems with the drawer are actually caused by problems with the printer. Try these steps:
1. Check that the printer has paper.
2. Be sure that the paper is inserted correctly. The paper should feed from the bottom.
3. Check to make sure that the ethernet cable is properly and securely connected to both the printer and cash drawer.
4. Check that the power cord is properly and securely connected to both the printer and the power outlet.
5. Try turning the printer off, then on again. You can do this using the power switch and/or unplugging the power cord.