2007WFP Will Not Enter Standby Mode

Hello,

I have a system running Windows XP SP3 with a Nvidia GeForce 7600GT and an ATI Raedon 2400 HD.  The GeForce card currently runs a pair of 2007WFP monitors and the ATI runs a single 2007WFP. The ATI monitor will not enter standby mode. The system enters the "Energy Star" standby after 10 minutes of inacitivity. The two Nvidia Monitors go into standby as expected; however, the ATI monitor will not. I have tried switching the monitors and the cables and the one panel will not go into standby. Instead of going into standby, the screen darkens and the little window pops up that says "No DVI-D Cable," and stays there indefinitely.

I believe this is a problem with the monitor. Other than not standing by, everything else about the monitor works perfectly. Is there a setting or something that I am missing?

Thanks for all your help/suggestions.

Evan