Answer:
bootrec/rebuildbcd
Explanation:
Several reason could have caused this, ranging from failed updates or installations to boot sector virsues etc
To fix this, you will need to restart the computer (Alt+Ctrl+Del) into recovery mode, Write the bootrec/rebuildbcd command and press enter or bootrec/fixboot.
If the task is successful, you will get a message "The operation completed successfully."
Then you are free restart your computer