have the other network cards (onboard) been disabled in the BIOS or disabled in Device manager?
I found the problem. When I disabled the old NIC's their DHCP lease was still in the system, The new NICs were given a new DHCP lease, thus two IPs were assigned the same computer name (though they had different MACs, of course). However, DNS was still linked to the old DHCP lease. I deleated the old leases and updated the DNS and everything started working.
Thanks anyway for you input.