How to rase CPU fan speed?

I have a Vantec copperX HS with a fan that is suppost to spin around 4000rpm but its only at ~2700rpm (confirmed with Sandra sisoft and bios). Why is that and how can I rase it to 4000rpm?

thanks

system spec:
Vantec CopperX @~2700rpm
P4 2.4b @ 2.7 (44'C idle 57'C loaded)
MSI 845PE MAX MOBO
512 2700
GF4 4200
Antec 830 case, 3 case fans
300watt

it may not be getting hot egough to make it go faster if its temp controlled or how ever its controlled isn't automaticly turning it up. find if its temperature contolled fan or a switch or what. then lmk~Alex

Does the mobo have fan control in the bios?