DVI-D port not recognized

[LSUfan71]

I have a HP 251-a123w  desktop that came bundled with a HP 22uh monitor.  Only a VGA cable was included but the HP 22uh monitor has HDMI, VGA, and DVI-D ports.  I've been using the system with the monitor connected with the VGA cable until Saturday.

On Saturday I shutdown the computer and connected the HP 22uh from it's DVI-D port to the DVI-D port on the computer using a DVI-D cable.  Then I connected an Acer X193w monitor from it's VGA port to the VGA port on the computer using a VGA cable.  I want to have a dual monitor set-up.  The HP support site for my model states that both ports may be used at the same time.

Well, my computer starts using the Acer monitor on the VGA port but the HP 22uh simply shows a "Signal Cable Not Connected!" message.  Nothing I've done will make the HP 22uh start on the DVI-D port.

I've updated drivers, I've restarted the computer several times.  I started the computer with only the HP 22uh monitor connected via DVI-D cable and still not recognizing the monitor.  I've uninstalled the display adapter then restarted, still doesn't recognized the DVI-D port (or maybe the monitor isn't recognizing the cable, I dunno).  I've powered down the HP 22uh monitor and started again, still nothing.

Any suggestions?   

[LSUfan71]

The DVI-D cable is a 6-ft DVI-D Dual Link Cable by Gigaware.

Is it possible that a Single Link cable is required?  The Dual Link seems to have extra pins and it does insert into the DVI-D port on the computer.

[LSUfan71]

Update: I verified that the DVI-D ports do match with the extra pins in the dual link cable.

Sorry for being such a newb on some of this stuff... 

[LSUfan71 · Accepted solution]

OK, dug the manual out of the garbage,  "Input Select option in the OSD menu"

Had no previous experience selecting input on a monitor...  Who reads the manual for a monitor? smh