First time installing (erasing Windows) from usb, did everything just so, Boot Device Not Found

Solution 1:

From your fdisk -l output you have Linux install in partition /dev/sda1. You need to ensure you have grub installed on that disk and boot to it. You might have to set your bios to boot to your first hard drive. The steps below is to install grub on the your first hard drive using the installed Ubuntu for the installation.

From your live session running these commands, one by one to resolve your issue.

1) sudo mount /dev/sda1 /mnt # (If your Linux were on a different partition substitute /sda1 for the partition of your Linux install.)
2) for i in /sys /proc /run /dev; do sudo mount --bind "$i" "/mnt/$i"; done
3) sudo chroot /mnt
4) update-grub
5) grub-install /dev/sda # (/dev/sda is the hard drive that has linux installed (i.e. /dev/sda or /dev/sdb ... etc.)
    update-grub

Now reboot the system.

If it fails to boot, perform the steps again, but this time be sure to also perform step #5 to install group on the boot drive.