My iMac no longer detects my apple external monitor

As a teacher, I moved classrooms this school year. After the move, my external monitor is no longer detected by my iMac. I've connected the cords just as they were previously. When I go to the Systems Preferences > Display, there is no Arrangement tab. Please help!

Hello cbecnel
There are a few things to try and they are outlined in the article below. One is to try a different cable and another one would be to try that display with another computer to help isolate the issue.
Apple computers: Troubleshooting issues with video on internal or external displays
http://support.apple.com/kb/ht1573
Thanks for using Apple Support Communities.
Regards,
-Norm G.

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Here is my standard reply:
#8 External Monitor Viewing.
Shane's Stock Answer #8:
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Hello,
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Message was edited by: Tw3aky

My iMac no longer detects my apple external monitor

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