GPT Partitioned Disk not Recognized by BIOS

Solution 1:

Are you sure you have setup the Bios to operate as UEFI only ? (Without legacy/CSM support.)
I've seen a couple of Bios variants that wouldn't accept GPT disks for UEFI boot if the legacy support was also on.

The logic seems to be based on the incorrect assumption that if you have legacy enabled your OS isn't UEFI capable and therefore also is MBR boot only. So the Bios doesn't even attempt to boot from the GPT/UEFI harddrive.

Weird thing is that those same Bios often do boot from an GPT/UEFI external media if you manually select that as boot-device. Makes no sense whatsoever...