@phant0mbot said in Dell OptiPlex 3000 Thin Client:

have tried both SAN and GRUB exit options

boot loader == snponly.efi

These are in contradiction with each other. SAN boot and Grub are bios boot methods. snponly.efi is a uefi boot loader. Since you are getting into the fog iPXE menu we can assume the hardware IS uefi based since it is booting snp.efi. Try a uefi exit mode of rEFInd (refind) to see if that will boot from the hard drive. The default value can be set globally in the fog configuration->fog settings page. Don’t force a bios attempted boot from a uefi booted computer, that never works.