XPS 13-9380, Ubuntu, no bootable devices found

I recently got a new XPS-13 9380 from my company HQ (we're a tech start up and do not have an IT person) that had Ubuntu 18.04 on it. I needed to take it back to Ubuntu 16.04 due to some programs that we use. I have a Ubuntu 16.04 bootable USB stick that I used.

I was unable to boot the the USB stick so I followed a Dell Community post to set the bios to boot to the USB stick. It involved turning on Legacy ROMs and using Legacy to change the boot sequence, it also had me change fastboot to thorough and enable Thunderbolt. I was able to boot to the USB stick and proceeded with the OS change back to 16.04, which was successful.

Upon reboot, I got (and have continued to get) an error screen saying "No Bootable Devices Found".

I went back into bios and it is no longer seeing the SATA HD as a bootable device, even though it is still listied under System Configuration. I changed the settings back to UEFI and unchecked the Legacy ROMs option under Advanced. I also changed fastboot back to Minimal. When I changed it to UEFI "Ubuntu" was not listed in the top portion of box as it had been on my first viewing of the bios when I originally changed the settings.

I am now able to boot into Ubuntu using the F12 button with the Ubuntu 16.04 USB stick attached to my laptop in the right USB-C port, but I still get the no bootable devices found error screen on a normal boot

Some things that I have also done to try and fix the issue is:  flashed the bios to 1..8 and put 18.04 back on the laptop.

Please help!!!