Have replaced EVGA 670 with ASUS 670 and bios is now visible (PS. PC was still able to boot into windows, bios/ POST had no display with "Error 51")
However, I have picked up another problem with the DX79TO series.
Unable to set memory to 1600, memory only works under clocked at 1066.
Intel DX79TO or DX79SI mainboard
Intel i7 3820, 3.6Ghz
Corsair Dominator 2 X 4GB DDR-1600 (CMP8GX3M2A1600C9)
ASUS GTX 670 2GB
Cooler master 1000W PSU
Sastec Technical Division
The link given by dave_g is the answer, but in reverse: new EVGA GTX 600 series cards have UEFI GOP-compatible BIOS, the DX79 boards BIOS do not support SecureBoot and GOP instead. So wait until Intel bring SecureBoot support for DX79 BIOS, until that use cards from other vendors.