maybe there is only one nic in the pc. maybe it is an unsupported nic. maybe the pc is broken. maybe the pc doesnt have enough irqs. maybe its installed wrong.
maybe the nics are the same kind and wont be recgnised as 2 nics. maybe one should try a different nic. maybe you should try a different pc.
if you gave a bit more info maybe someone could help. maybe you should read the manual.