What Causes USB Ports Not to Work?

Some causes relate to the previous device connected to a port. Microsoft's website indicates that USB ports may not work after you connect a defective accessory to the computer, even after disconnection. To correct this, shut down the computer and start it up again. Another problem is that rapidly connecting and disconnecting an accessory might cause the USB port not to work. Reconnecting the device and scanning for changes to the hardware, restarting the system or resetting the USB controller may correct this problem and make the ports work again, according to Microsoft.

Other major causes of USB ports not working include invalid software and operating system settings. The problem may stem from these settings if you recently added a new port or device, installed a new operating system or made other significant changes to the computer. Settings in the Control Panel, Device Manager or main setup program may prove necessary. It's also possible that the computer still needs drivers for the USB port, device or controller. Additionally, the computer could have a virus that interferes with the work of certain accessories or ports.

Although issues with software and accessories tend to produce more computer problems than actual hardware failure, it cannot be ruled out. If the computer uses a USB card installed in one of the expansion slots, it could have become loose or the slot might have failed. A wire running from the USB port to the motherboard may be detached. Other potential hardware causes include damage to the ports or a defunct USB controller. It's also possible that the ports simply need cleaning.

Connecting the wrong type of USB extension cable may cause the ports not to work. Using a high-speed accessory with a low-speed USB cable causes this to happen, according to Microsoft. Some old operating systems do not support USB, so the ports will do nothing more than supply power to an accessory. For more possible causes, refer to the instruction manuals of the computer, the accessory and any add-on USB hardware.