Aurora R4, video card swap, boot issue

I have an Aurora R4 and just removed 2 x GTX555 (sli'd) -and fitted a single 2Gb Nvidia GTX770 2GB graphics to test the card-but I did not uninstall the old drivers! Now the pc is stuck at the Alienhead boot screen but nothing happens when I press these keyboard buttons . Is there anything I can do to recover this? Re-Installing the 2 x old GTX 555's cards just gives a blank black screen -I don't even get the Alienhead bios screen etc. BIOS is very old AO3, latest is A11 and assume this is the problem not recognising the new card. Understand the BIOS has to be updated through the various newer versions (which I have on my pc ),but cannot find a way to do this can any one help out here?-understand it can be updated by using a bootable usb stick (Rufus prog) but confused on what to do at the boot screen UEFI choice etc and don't want to brick my motherboard Thanks in advance :) Also is this pc capable of running one of the newer cards i.e Nvidia 1080/ti or 2070?- do not want to go down the Radeon route.