The scanner hasn't been turned off by any chance?
If not....you could try
Start Type in Administrative Tools Click on Administrative Tools Click on Component Services Click on Services - Local
Scroll down to see if UPnP (universal plug and play) has become disabled - if it has click on that and enable it.
If this doesn't help check to see if your scanner needs an updated driver.
Check that the usb lead hasn't worked loose - try it in another port.
You could consider uninstalling and reinstalling it, letting Windows find the driver.
It may be happening as a result of a recent update - if all else fails you could restore your PC to a time before you started to have the problem.