I would recommend to check for power going into both the high and low speed fan relays. I believe power comes into these relays via red wire. If there is power to these relays, I would recommend to check to see if these relays activate and power up the fans by grounding the light green and violet wire coming into the relays from the computer.
SO if this is the case, then we simply have a break in the wiring from the relay to the fans.
DO you need a diagram?
Would you like a wiring diagram?
Does this make sense? If not, please let me know.
Here you go.