Things to try...
1. Unplug PC from power outlet. Press the Power button. Wait 2~5 minutes. Plug back in to the wall and boot up
2. Force the OS to detect your device using Device Manager. Go to Device Manager, highlight your computer (the very top of the root), right click and select "Scan for Hardware Changes".
3. Disable Windows USB power management. Same place, Dev Manager, find the "unrecognized device", right-click, properties. Power Management tab and uncheck "Allow the computer to turn of...". Unplug and re-plug device. Repeat step 2.
4. Use system restore to roll back to when it used to work.
5. Run System File Checker. Start>All Programs>accessories. Right click on "Command Prompt" and pick "Run as Admin". type SFC /SCANNOW. Post the results here.