1. sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update  

2. sudo apt-get install -y boot-repair && boot-repair 

3. Then, you can see the followings window: 

==>> Recommended repair

Do as the windows asked. 

 4. Sometimes, you may also enount errors as follows: 

well, just reboot and try to use USB to repair this time.