When you run automatic startup repair via Windows 10 Installation disk (DVD/USB), it shows the error in trying to fix master boot record;
Automatic Startup Repair couldn’t repair your PC
Here’s how you can fix this issue.
Insert your Windows 10 installation USB or DVD and boot up your computer by pressing F12 to select boot media (external);
Click on “Advanced Options” and select “Command Prompt”
Run all of these commands irrespective of the results;
Now reboot your computer to see if it fixed the issue. If not, then run this command in the Command Prompt via Advanced Options;
chkdsk /r c: