The most common cause of issues by far is a cable not being connected properly, or a piece of equipment simply not being powered on.
The most frequently received support requests are reports of ‘Cash Drawer Not Opening’. It’s important to remember that the cash drawer is operated by the receipt printer, regardless of whether you are actually printing receipts or not. Cash drawers are very durable pieces of simple mechanical equipment that rarely fail, it is usually the cable from the cash drawer to the printer has become disconnected (the cable will usually fit in two holes, it’s important to put it in the smaller one, usually marked ‘drawer’), or the printer is powered off or is itself disconnected from the till. The printer must be powered on for the cash drawer to open.
Most other issues such as ‘blank screen’, ‘no lights on’ on any equipment, are almost always cable related too, disconnecting and reconnecting cables, ensuring they are connected properly, and ensuring equipment is connected to the mains power socket and that the socket itself and any extension leads themselves are turned on, will usually rectify any such issues.