Repair Booting Ubuntu and Windows

Step 1: Boot from Ubuntu USB Stick

Step 2: Install boot-repair

$ sudo add-apt-repository ppa:yannubuntu/boot-repair
$ sudo apt-get update
$ sudo apt-get install -y boot-repair && boot-repair

Step 3: Run boot-repair

$ boot-repair
Choose Recommended repair
Note down paste.ubuntu.com/XXXXX URL if any error

Step 4: Reboot, Restart your Computer

Even if any error, just try.

Step 5: Done

If it worked you can now boot into Ubuntu and Windows with GRUB (Boot manager)

Links

https://help.ubuntu.com/community/Boot-Repair

Utils

List installed Partitions
$ sudo fdisk -l

$ boot-repair

$ gParted