you should try going into the BIOS and see how to enable the top slot ( make it first. )
be nice you list all your hardware when posting.
what mobo are you using?On Most the top pcie slot is for the primary card,and monitors in a crossfire setup have to be plugged into that(primary) card only.
Sometimes Crossfire will just choose which card will be primary... Mine chose the middle of my three for some weird reason, and I can't change it. No matter what order I put them in, it's the middle one. I suspect yours is doing the same, and you'll just have to put up with it.