To save energy, Windows automatically turns off the power to the USB ports. It certainly saves energy, but what if it’s causing you problems with additional devices or you just need a USB device that’s always powered?
Power management is also a common cause of problems with connected USB devices; if Windows can turn off your USB controller, sometimes it won’t be able to turn it back on properly, which will interfere with some USB devices (especially scanners, cameras and some phones like Blackberry).
Prevent Windows from shutting down USB devices
To prevent Windows from “managing” power to your USB controller or devices, do the following:
Open Device Manager by typing Device Manager from Start Search.
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The Device Manager window will open. Expand the Universal Serial Bus Controllers branch, then double-click the USB Root Hub device and select the Power Management tab.
Disable the Allow the computer to turn off this device to save power setting by clearing the check box, then click OK:
Repeat this step for each USB Root Hub, or only for USB ports that must be enabled at all times. If you lose USB connections or power from the USB port to an accessory device, try the above steps, then unplug the device and wait a few minutes to see if the problem goes away.