There are several instances in which you might need to test your USB port. You might have built a computer and need to see that the port is properly connected, or a drive you had plugged into the port could have suddenly stopped working, and you need to determine the cause. Using a simple loopback test, you can see if the fault is with your USB port.
Insert the loopback plug software and install it on your computer with the USB port you need to test. This step might not be needed if your plug has a "plug and play" feature that precludes it from a separate software installation on your computer.
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Insert the USB loopback plug into the USB port. If it is plug and play, the software will automatically download onto your computer from the plug.
Look at the lights on the loopback plug. Referring to the owner's manual for the plug, compare the lights to the list in the manual. The colors of the lights will tell you if the USB is getting power and if it is sending and receiving information.
As an alternative method of testing your USB port, plug in a plug-and-play mouse or other input device.
Move the mouse to see if the cursor on the computer responds. If it does, the USB port the mouse is plugged into is operating properly.