Unfortunately I have to replace the old board into my client's machine each time I try and fail miserably to make it work, so it isn't currently plugged in and running to inspect the BIOS version... I did try every combination of boot order, CSM settings though.
I'd be grabbing an ATX power supply, splatting the board on something non-conductive and spinning it up to test *before* putting it in to the clients machine. That way you can test things easier *without* taking the current box offline or going to site to do it, and work out what's going on.
Also, check that you've actually got the ethernet boot rom enabled to allow PXE booting.
Thanks,