When you start your Windows 10 PC and got an "Operating system not found" error or just saw "Auto repair for startup" or a blinking cursor with black screen. A loop for Auto repair will start but fix nothing. You will be panic as there are no backup of your document. How can you fix the problem?
Of course, you can run a reset to factory restore in Windows 10, but you need to load back all installed applications and your current working document might not have a backup and to need to do all customized settings again.
In the old days when you were using Windows 7, you could fix the problem by starting from a MS Windows Setup DVD / USB or Recovery Disc and run Command Prompt to execute bootrec command to fix the bootloader. So, you try the old ways and it does not work on Windows 10.
The question in the link below is a recent problem which I have participated to solve.
Disable UEFI in BIOS, boot from win 10 setup DVD or USB and follow the instructions below.
First, you are asked to choose your keyboard layout. Press the layout you want to use. If you want to browse through the available options, press "See more keyboard layouts" until you find the one you want to use.
Choose an option of Troubleshoot. In the Troubleshoot screen, press Advanced options. In the Advanced options screen, press Startup Settings. You are informed that you are about to restart in order to change several Windows options, including enabling Safe Mode. Press Restart.
Your computer or device restarts again and displays nine startup settings, including Safe Mode, Safe Mode with Networking and Safe Mode with Command Prompt. Pess the F10 key for more option and press the key for Launch Recovery Environment and click Restart.
On restart, you will enter Windows Recovery Environment and select Advanced Options and select Command Prompt.
In command prompt, type the lines of command below. bootsect /nt60 c: /force /mbr bootrec /fixmbr bootrec /fixboot bootrec /rebuildbcd Press enter after typing each line to execute.
Restart computer and go to Windows Recovery Environment to run "Auto repair for startup".
The Lesson learnt
You need to launch Windows Recovery Environment again after starting the computer is Safe mode to run the bootrec command and it is only possible to fix it when you boot from the OS, but if you do a normal boot, you cannot enter windows recovery environment.