TamedKnight

I have a fan that has only a molex connector. My psu has a cable that ends with a molex and a 3 pin header in unison which can be used to connect the fan to the motherboard. But if I have the fan connected and try to start my pc it simply doesn't work. I must unplug it to be able to start it. Could anyone help me? My mobo is brand new so I'm pretty sure that's not the issue.