If your GPU doesn't work now with a clean install then likely you have suffered hardware failure. Likely the GPU, if not the Power Supply or even potentially the mother board. Best thing to try is your card in another machine or a different GPU in yours to narrow down what is wrong.
Oh since you mentioned you have crossfire try one card at a time and test in each motherboard slot one at a time. You can figure out if it is the board slot or card this way.