Problem with Dell Ultrasharp U2412M DVI Connection

I have a Dell Ultrasharp U2412M which I purchased from Buy.com on 1/23/2012.

The DVD connector stopped working some time ago and I would like to find out what options I have to have the monitor fixed or replaced.

The DVI connector worked originally, then one day it just stopped working.  

I've tried connecting several different computers with different DVI cables and the monitor never detects any input on the DVI input.

Connecting a different monitor's DVI connector to these same computers/cable works.

The monitor's DisplayPort and VGA connectors are still functioning just fine.

Please let me know what steps I need to follow to get some warranty help with this monitor.

Thanks!

Alan