So I have a Tyan S8225 motherboard with a Valencia (Opteron 4200) CPU.
Two of us have tried everything. We have even swapped the whole motherboard, Power supply, memory, even a different CPU (still Valencia). We even tried it without any memory installed and with only a single CPU. There are no beep codes as I suspect even those are controlled by the BIOS boot process. We put the whole thing on the bench with just the power supply, VGA, keyboard and network (for IPMI) connected.
The IPMI is not even showing the BIOS starting, but the IPMI is working.
After some hunting around, I discovered the claim on the website is that the Valencia CPU's are not supported on older BIOS revisions. For a start, I don't know what the bios revision is and if it's older but it's the only thing left.
Could the BIOS be causing a board not to boot at all? If that's the case, then is there any other way to update the BIOS without buying an old CPU only to be put back in a box just to update the BIOS? Yes, we even tried updating the BIOS through IPMI but you can't do that either.