Hello and welcome to the forum.
Boot your computer from the installation media.
The installation media can be obtain through either of these two resources.
https://www.microsoft.com/en-us/software-download/techbench
OR
http://www.microsoft.com/en-us/software-download/windows10
Once you have the ISO, you can use ImgBurn to burn it to a DVD or Rufus to burn it to a USB ThumbDrive, either of which you can use to boot your computer.
Use the Repair Your PC link on the second page after booting and try using some of the Advanced Troubleshooting options available.
You could try a restore point or worse case a reset.
You should probably make every attempt to backup any critical data that is on the disk before going forward.