Every so often, a USB device fails to be recognized and usable even though it has been connected for as long as the PC has been running.
Using the USB cable
1. Unplug the USB device and wait for Windows to signal the disconnect, or for 30 to 60 seconds to be sure Windows knows the device is gone.
2. Reconnect the USB device and wait for Windows to recognize it again.
Using a graphical user interface
1.Click Start, then right-click My Computer and select Properties.
2. Select the Hardware tab, then click Device Manager.
3. Locate and expand the USB device, right-click on it, then select Properties.
4. If the device properties dialog includes a power management tab, click on it.
5. Uncheck the box next to Allow the Computer to Turn Off This Device to Save Power.
6. Click OK, then close Device Manager.