P5B Deluxe USB problems

Hi, I have an ASUS P5B Deluxe motherboard, the usb ports on it do not work (don't detect anything). I seen many other people with this problem when searching for solutions but nobody seems to actually know what causes this. I have two of these boards (one has a very damaged cpu socket so I will use it for parts).
Does anyone know what actually causes the usb ports to fail on the 1.03G revision of these boards (apparently not the 1.04G). I have already replaced some capacitors on the board (NCC KZG, know to be a bad series of caps) but this doesn't solve the problem. The board boots fine but doesn't detect any usb devices.
I would appreciate it if someone would let me know the cause of the problem.
Thanks