Boot from the original installation media
At the Welcome screen, click Repair your computer
Choose Troubleshoot
Choose Command Prompt
When the Command Prompt loads, type the following commands:
bootrec /FixMbr
bootrec /FixBoot
bootrec /ScanOs
bootrec /RebuildBcd
Press Enter after each command and wait for each operation to finish
Remove installation media
Type exit
Hit Enter
Restart your computer and check if Windows 10 can now boot