Enermax PSU beeping problem

[Ricard]

I've recently built myself a new PC, and I chose an Enermax Galaxy 850W for the power supply. Everything works fine, until I try to play Oblivion. The PSU flashes and beeps at me, but stops when I exit the game. The manual tells me that the problem corresponds to a "PSU fan fail warning (Fan RPM < 450 RPM)". I've tried three other games, all with no complaints.
Chances are, the problem will crop up with a few other games I decide to install in the future, so could anyone help?

 

[Ricard]

Thanks Meatloaf. As delbuenno said, I meant the warning LED.
In a way I've already tried disconnecting the the PSU fan monitor, as I had left it unconnected when I finished building since I wasn't sure what it was, but then connected it afterwards. It still beeped then.

 

[Ricard]

Okay, I've just had a look in the BIOS. It shows CPU fan speed and chassis 1-3 fan speeds. Each chassis fan speed shows N/A, but that'll be because my case fans are connected via 4P Molex. There doesn't seem to be any mention of a power supply fan. Do you think connecting the PSU fan cable to one of the empty chassis fan connectors would work? If it helps, my motherboard is an Asus P5K3 Deluxe.

EDIT: Okay, I went ahead and connected the PSU fan cable to the chassis 1 connector. The BIOS is showing an RPM of around 1800, which is obviously a lot greater than the 450 RPM the PSU thinks it's going below. However, trying to play Oblivion still results in the PSU giving the same warning. It seems to be a problem with the PSU detecting its own fan speed.