Does the device work in another computer?
Do other devices work on your computer or is the problem with just this one device?
1) device bad
2) USB driver is corrupted, or gone MIA
3) the USB port is either damaged or the contact pins are no longer making good connection. Note: USB ports can be damaged if overcurrented. they are limited to ONLY 0.5 Amps (2.5Watts) for USB2. USB3 has a higher output capability.