I have a MacPro 2008 3,1 model running 10.10.3; I've upgraded the video card to a Radeon R9 270x (flashed professionally for use). It's fast. Very fast. However, on boot-up, I get the EFI screen which then goes black as soon as OS X loads. If I disconnect the display and reconnect...hey presto! everything works (screen not black).
Is there a work round so I don't have to do this physical disconnection/reconnection?
The video card is this one (see below) which also shows the display type.