One common problem we get is that people ring up about issues they have with their receipt printer. Since the cash draw works from the receipt printer, if the receipt printer does not work, then the POS system does not work either on that computer.
Firstly, check that there is enough paper, that everything is closed. If all this looks okay, next switch the receipt printer off, wait say 10 seconds and afterwards switch it back on again. If this does not fix the problem, then check the cables are firmly in. Normally, there are three cables one goes in the cash drawer. The next is for the power. The other goes to the computer. I find taking them off and putting them back it, often helps. After you do this try turning the receipt print off and afterwards on again. Now if it still does not work, now give us a call.