replacing the etherfast PCI adapter

I have installed a new etherfast PCI adapter in my dimension dell 4600 computer I am trying to hook up the router to my other computer. The other computer says its enable but my says disabled and won't let me hook it up or won't reconize it. After I have installed the new PCI do I have to go to Bios and disable the old one in order for the new one to go into effect? How do I do this ? If this is the problem. Not real sure if this is the problem. I would appreciate any help. I am not a computer whiz. Please advise!!