i had this problem and i fixed it. i faced this after updating my win8 and rebooting after that update.
to fix this, i tried safe mode but it failed to boot. finally i tried to boot with "force drivers to have signature disabled" and it worked.
How do you do that??? I have tried to do everything but I don't know how to get to that part.
Based on your PC or Laptop, you should press F8 or F6 or F2 or F12 just after you turn on the device, this is how you will be redirected to advanced boot menu options.