I decided to wipe my Windows 10 installation and to use Ubuntu from now on.
I followed a guide that instructed me to wipe all previous partitions on the HDD and then create / and swap and install. I also had to create the EFI partition.
After doing all the above process I rebooted my laptop. After POST it showed "No Bootable Devices Found".
I figures out that GRUB wasn't installed so I proceeded to manually install it. I still got the same error.
I then ran Boot-Repair to try and fix my problem. It create a pastebin. I still can't boot to Ubuntu.
Looking at GParted, all the flags seem to set correctly.
Where am I going wrong? I've spent hours with a friend trying to diagnose this but we both are clueless.
EDIT: When I plug in my bootable drive and select "Boot from another volume" I can see my HDD and boot from there into Ubuntu.