I'm having this same issue, but no matter what fan I put in the case, it's just not working. I've reset and updated my BIOS, and I have no option in there for fan control. There are no other connecters on the mobo for the fan. The motherboard I'm using has the three-pin connector. It is also an older Model HP, but I can't tell which model exactly anymore because it's no longer in its original case. I've switched out everything but the motherboard itself (I don't have any other working ones...) and there's still no change. Could it be the connector itself on the motherboard? If so, would I have to do some soldering? I'm at wit's end over this one....