take everything out of the case except your powersupply, and make sure its plugged into the wall
it has the 12x2 molex connector (the big one that plugs into the mobo)
find the green and black wires, they should be adjacent (There are usually multiple black wires, so make sure you use the adjacent green/black!)
fold a paper clip, and stick both ends into the green and black wire holes
this will jump the power supply like a switch
now you can use the 4x pin molex connectors on the power supply for fans