Rx 480 Nitro 8gb - bios not finding was working

Rx 480 Nitro 8gb on an Asus Sabertooth mobo. I was playing wow then pc cut out, boot gives beel code "-. . ." which is no video card detected. punched in my 5770 HD and get into windows fine. Cannot boot into windows with both cards for some reason. Removed 5770, put in rx 480 and able to boot in (using usb monitor to actually function in windows). Attempted w/ bios switch switched in either mode, no change. Need advice on what to do... RMA will literally kill me if thats my only choice.