Is your monitor plugged into the card or the board? The board video could be disabled when a card is plugged in.
It's plugged into the board - I guess this is disabling the board video and is the problem - is there a work around?
You are plugging the PCI-e connectors from the PSU directly into the cards correct? Then using a molex from the PSU to power the riser cable with the connection on the riser board? You need both. Should be a 8 pin and 6 pin connection on the card that needs to come directly from PSU, and then a 4 pin molex on the roser board that comes from PSU.
This is what I've done yes.