Ethernet Port 2 does not work

Hello folks,

Internet, file sharing and screen sharing all work on Ethernet Port 1.
None of these work on Ethernet Port 2.
Would anyone happen to know how to fix this problem?

Thank you for reading through this.

What kind of Mac, is port 2 hooked up, etc?

My apologies for giving too little info.

Using:
Mac Pro 2 x 2.8 GHz Quad-Core Intel Xeon
OS X 10.5.7

Ethernet Port 1 is fully working, for connecting to the internet, file sharing, screen sharing, etc.

Ethernet Port 2 is not working, for anything what-so-ever.

Thank you for taking the time to looking this through.