DHCP problem

I got a problem to setup a new DHCP on a new NT server.

At DHCP Manager, I tried to add a address of DHCP server. When I click Ok. Error cameup as:

Unable to connect to DHCP server at x.x.x.x.
Server may be down, or DHCP service not started.

I checked DCHCP service is running and NIC is running also. IP already entered in DHCP Relay on TCP/IP properties.

Server runs on NT 4.0 with service pack 5.

One thing I supected:

When I installed NT, I could not install the NIC becausethe driver need sp5 or higher. So
I installed NT with MS Loopback Adapter, and then updated NT with sp5. I came back to install the NIC adapter and then removed MS Loopback Adapter.

Thanks

Edd