1) go to your start menu.
2) press power button.
3) HOLD the shift key on your keyboard and keep it held while you click restart.
4) Select Troubleshoot>Reset this PC>Remove Everything
5) When prompted, select Just remove my files. do not select fully clean the drive.
if that doesnt work, get a usb and use the tool to create a full installer of windows.
heres the program that will guide you through creating the installation to your usb:
http://go.microsoft.com/fwlink/?LinkId=691209