Power on and off your computer three times
On the third time, your computer will boot into the Advanced Recovery environment
Click Advanced Options
Click Troubleshoot
Click Advanced Options
Click System Restore, see if you can go back to an earlier time.
If not, boot into the recovery environment again, then try performing a startup repair.
If that does not work, boot into the recovery environment, then click 'Go back to previous version of Windows'
If that does not work.
Go to a working computer, download, create a bootable copy, then perform a clean install.
Step 1: How to download official Windows 10 ISO files
Step 2: How to: Perform a clean install of Windows 10
If there are files on the drive you want to recover, see - How to: Perform a Custom install of Windows 10