Cause - Both network ports are enabled
1. Disable one of the NICs in the CMOS setup utility. PXE boot will then proceed without the request to choose which NIC card to use.
2. Upon powering the machine, press delete repeatedly until the CMOS Setup Utility appears.
3. Navigate to the Chipset heading, then choose Southbridge Configuration. Highlight Onboard LAN1 Boot and set it to disabled.
4. Navigate to GbE LAN1 Boot and set this to disabled as well. Press F10 to save changes and exit.
5. Restart the machine and press F11 to boot from LAN, and PXE boot should function normally.