one more possibility, you may need to update your mobo chipset drivers.
do you know the manufacturer/model of your motherboard??
this info will help us provide you with motherboard chipset driver and bios setting recommendations.
if you dont have any docs with that info take the case side off and look for markings on the motherboard.
another alternative is to download sisoft sandra and look under the motherboard information tab.
http://www.sisoftware.demon.co.uk/sandra/