Start System Recovery Options if you're using Windows 7 or Windows Vista. At the prompt, type the bootrec command as shown below, and then press Enter : bootrec /rebuildbcd Rebuilding the BCD in Windows should only take around 15 minutes: Start Advanced Startup Options if you're using Windows 10 or Windows 8.
You may need to choose your account name and enter your password to get to the Command Prompt. If you can't boot into your Windows 10 system or don't have the original installation disc, use Easy Recovery Essentials and run Command Prompt Your computer will show a Preparing screen for a short time while it readies the computer.
In Windows 10 you can access the bootrec.exe utility by using your original installation media: DVD or USB drive.
