The process we have been using to boot Dells to the K2000 imaging server requires PXE boot in “Legacy” boot mode. The optiplexes we received in the summer of 2017 came with “Secure boot enabled” and UEFI boot set in the BIOS.  The following three BIOS settings had to be changed to get those models to boot PXE to the K2000 deployment server:

— Disable “Secure Boot” — (you may need to reboot to have this setting apply)

— Enable “Legacy ROM” —

— Select Legacy Boot not UEFI Boot —