Cant log into Network

I have about 25 PC’s logging into a Windows NT Network, useing 2 hubs and 1 switch. I now want to move an old computer to a new location on out Network. The problem is that I can plug into one port and the computer works, but if I take it to this new location it will not log into the Network. I have tried all the obvious things like cable,line problems and everything works fine. I can plug the old PC into the new location and it works, but the new one will not work at the new location. Theweird thing is that the new computer will work at another port?? So it seems like that port will not except that new computers network card. Any idea’s??