Asus mobo and fan speed

Bonjour,

I have an ASUS P5WD2 Premium motherboard and a pentium D processor.

I can read in the manual: "If installing a dual-core CPU, connect the
chassis fan cable to the CHA_FAN1 connector to ensure system stability."

It wasn't like this when I bought my computer, so I have done it now but
now the CPU fan speed no more changes whatever the temperature of the
CPU is. Before I connect the chassis fan to the motherboard 3 pins plug
CHA_FAN1, the CPU fan speed increased while the temperature was going
higher and higher.

What is wrong now?

BTW, I have seen on the ASUS web site that there is a new BIOS for this
mobo, but the specified OS are only windows OS. The previous version
specified "all". Is there any danger to flash my BIOS with the latest
version?

Thank you.
--
François Patte
Université Paris 5 - Paris
.