Performing System Restore takes too long to finish

Hi All need some help, please. I am restoring my pc and i am taking it back too factory setting how it 3 years old and i have a white screen with a gray box in it with an icon of a pc with a magnifying class running around it how its been doing this for 12 hours now and the line in green is moving faster now does anyone know how long it will take or can i stop it?
