Whenever you encounter a problem with your Computer, Windows, Internet,
anything, always shut down Windows properly (if possible) and turn
everything off. Wait about 30 seconds then switch everything back on.
In most cases this will solve your problem.
Hold down the power button of your Computer (not the Screen, but the tower) for at least 5 seconds and the Computer should turn off. Please only do this if you absolutely cannot shut Windows down properly as this can lead to a corrupt hard drive and loss of data.