About boot-repair:

Having troubles with the GRUB bootloader?
Download a Linux image of a kind. I suggest Linux Mint.





Move it to a RAM stick or a DVD.
Then boot up the LIVE system, and run this in the Terminal:

  ~$ sudo add-apt-repository ppa:yannubuntu/boot-repair

Now install the boot-repair entering this:

  ~$ sudo apt install boot-repair

Then when you have installed the tool, run it:

  ~$ boot-repair

A small window will open, with the option to click on a button with the caption: "Recommended repair (repairs most frequent problems)".
Click that button and let the program do its thing.