Computers use network cables to communicate with each other. They also use cables to communicate with printers, barcode readers, data-collection devices, etc.
Cables usually consist of bundles of wires. Each wire is connected to a contact (i.e., pin) at both the computer and the external device.
If a wire breaks, or has an intermittent connection, the cable may simply fail to work. It may also appear to work properly, but in fact be corrupting the data that it carries.
If the computer does not appear to be communicating properly with an external device, check the cable, including the connections at both ends.
If there is any doubt about the reliability of a cable, replace it.