GA-7N400 Pro2 not finding SATA disk due to front fan problems!

Hi,

I had a strange problem with my new GA-7N400 mb the other week.
When I had installed the system I was not able to install windows on
my new SATA disk. I went into the BIOS and disabled the SATA RAID
function. However, when I had done this the PC would halt halfway
through the boot at the BIOS page where the SATA harddisk detection
occured. My new Samsung 160GB disk was not detected and the BIOS would
not pass this stage.
I took the motherboard and disk to the shop where I had just bought it
and there, bare on the test bench, it would start without any
problems.
Puzzled I returned home and rebuilt the system, but this time with
only the basic devices connected. To my amazement it started again.
However, when I attached all devices the mb got stuck at the boot just
like before.
After some detective work I found that the problem occured when I
attached the old fan in the case front to the auxilary motherboard fan
connector. I verified this a few times and it was certainly the
problem.
The fan (I think it was a quiet fan from Evermax? with temperature
sensor speed control) is a good year old, but worked fine in my old
MSI KT7 mb. With a new fan from Arctic cooling this problem does not
appear and the mb has worked well since.

Has anyone seen a similar problem and/or can someone explain how this
happened.
Was there a problem with reading the fan speed that stopped the boot
as a security measure?