The easiest way to know if Xfire is working is to download GPU-Z and look at the bottom where it reads, "ATI CrossFire" and make sure it shows "Enabled (4 GPUs)"
lol, a little late bystander. he already discovered that crossfire is not working.
it should work on the board, so try looking for a BIOS setting. if not, try as Rofl_ said and individually check to make sure the cards are not defective.