CPU fan shot, PC won't boot

I had an older emachines system that I had gotten from a co-worker and decided to fix it up and give it to my room mate since he has no computer to speak of.

I've checked every part by swapping them all out into another PC and everything works fine. The problem is that the connector for the cpu fan on the motherboard is shot. I've tried 5 different fans that all worked fine on another system yet none work on the emachine.

I have a fan on the heatsink that connects to the powersupply via a molex connection. This powers up the fan when I turn on the PC but it's still shutting down since no fan is being registered as connected by the motherboard, I just get the standard cpu fan failure message and it shuts down.

Is there a way to override this?