This will occur at boot if the following are true:
Boot to LAN is enabled in BIOS Setup.
A network cable/connection is not present.
Network Boot is in the boot order before a present boot device.
Am always amazed at the timely amount of accurate information you have! Wow! Anyhow, Option 1 and Option 3 are disabled! Well, probably option 2, sad to say, the network cable/connection is always present and the RJ-45 plug green LED is always ON and the Network connection icon in the "system tray" is available! How about the system unit pushed;moved! Can't is cause the hard drive to slip away from it place since mine is not well fixed hence the "Media Test failure" and attempts to boot from PXE?
(My hard drive is not fully enclosed beneath, it exposes the circuitry). How about the ribbon cables, they appeared crumpled and squeezed between the drives?
When I tried to straighten them, and fired-up the system, this time it could boot! For other cases I just tried to place the hard drive in the right position and the system could fire up! Probably I need to fasten it with screws to the chassis!