how to fix Windows 10?

You could always try to roll back to a previous restore point - seee this article:

http://windows.microsoft.com/en-gb/windows-10/windows-10-recovery-options

If you have not dpne anything that creates a restore point the simplest expedient would probably be to use the media installation tool and create the appropriate install media; either a CD or a USB stick.

Make sure you make a note of the Windows product key

http://windows.microsoft.com/en-us/windows-10/product-key-windows-10.

Install media can be created using the media creation tool you will find at the bottom of this age:

https://www.microsoft.com/en-gb/software-download/windows10

Here's a few more notes:

http://winsupersite.com/windows-10/windows-10-clean-install-using-media-creation-tool#slide-0-field_images-57241


USB Media creation notes here:

http://www.thewindowsclub.com/how-to-create-bootable-usb-media-from-iso-for-windows-10

Once you are up and running, make sure you create a backup

Loads of info out there. All you have to do is search FOR YOURSELF
February 2016