It has never worked with my current computer. (Surface Pro 3)
It's a HL-340 USB to RS232 Serial Port Adapter with an Aruba serial to RJ45 connector and a cat5 cable.
I've got;
2 x usb to serial adapters
2 x serial to RJ45 cables
1 x serial to RJ45 connector
lots of cat5 cables
I've tested various combinations of the above to no avail. Also tested on another laptop and other APs.