Dual NICs that don’t work together on a Windows 2000 server

I have two NICs that connect to two separate internal LANs.

One NIC has a direct connection to another server. The other one is connected to a patch panel to connect to the rest of the computers in the same domain.

The thing is when both NICs are enabled on the windows 2000 server, it was noticed that the network connection for the NIC that is connected to the domain would lose its connection to the rest of the servers in the domains after a while.

No other servers in the domain can be pinged to the server, and vice-versa. The gateway can be pinged though.

The other NIC continued to work fine.

Anyone know how to troubleshoot the problem? Or anyone know what is the problem?