Which slot did your put the GPU in? The blue slots run x16... The black ones only go x4 or x1.
EDIT: Wait, nvm wrong board.
Found this: http://www.techarp.com/showarticle.aspx?artno=522
Might help
EDIT: Wait, nvm wrong board.
Found this: http://www.techarp.com/showarticle.aspx?artno=522
Might help