Does any one how to get a dual processor to work?

I have asked this before but still no dice. I have an Intel Core2 Duo 2.4Ghz and a motherboard that supports it but it is only running 1 core. How do I get both cores running? I am running Windows XP Prof. \ Motherboard: ASUS P5N32-SLI Premium \ 2 gigs memory \ eGForce GTS 8800 \ Sound Blaster X-Fi Gamer. Need more info let me know. Thanks in advance.