Sorry, but you don't flash biosses under LN2, it's a good tip... I've had some issues with this board under cold and would never flash it at them temps man.
only thing you had to do was to shut down the PSU, boot the rig in OC failed mode, go into bios via F1 and save the bugger then all was back to normal...
This is not 100% the board to blame Thijs man... you messed up too here
Try popping the battery, or inverse it in the socket... and then try again.. hope you can revive her...

