Problem: Cash Drawer does not open.
First, check that the cable is connected firmly in both the cash drawer and the receipt printer. Many cables are one way; check that if the ends are labeled, that the side labeled cash drawer or C/D is in the cash drawer.
If it still does not work, then it depends on the setup of the receipt printer:
For a USB printer, the cash drawer is controlled by the driver. Where depends on the exact model, but go to the printer driver in windows and set it. Print a receipt and check if the drawer will pop.
For a serial printer, note that there is a known issue where the cash drawer will not open until at least one receipt has been printed. You should double-check the setting from the invoice screen under tools -> options. On the printers and hardware tab, verify that open cash drawer is checked and that the command is set correctly; use 27,7,11,55,7 for most star printers and 27,112,0,25,250 for most Epson-compatibles.