Sometimes when you’re installing another OS like Linux on a single disk drive with Windows 10 on it, the boot record got overwritten or corrupted which makes it unable to load Windows and you just want to restore to its original state like before.
For this fix you need the original Windows 10 DVD installation disk to repair the Master boot record.
1. Place the Windows 10 Boot Disk in your DVD drive and boot from it.
2. When the Welcome screen loads, click Repair your computer.
3. Then choose Troubleshoot, then choose Command Prompt.
4. Type the following commands pressing Enter after each line:
bootrec /FixMbr bootrec /FixBoot bootrec /ScanOs bootrec /RebuildBcd
5. Wait for each command to complete.
6. Remove the DVD disk, type exit and press Enter.
7. Now reboot your computer.