U2412M worked fine for about 5 months and all of a sudden has a green vertical line. 

I followed steps to reset to factory default, also unplugged power and DVI port, waited 30 seconds and powered on. Green line remains. Ran BID and it shows on grey, red, white screens. Answers to question in FAQ:

* What is the 20 digit alpha-numeric monitor serial number and A0x revision?  
CN-04V35D-QDC00-782-107S  A04
* To what computer model is the monitor attached?
MacBook Pro 13"
* What video card/GPU is in the computer?
MacBook internal GPU, HDMI port to DVI
* What video out ports are on the video card/GPU or computer?
HDMI w/ DVI adapter
* List all monitor cabling attached to the computer and the ports they are using
HDMI w/ DVI adapter
* What Windows power plan? Example = High performance, PCI-e Link State Off
Not Windows
* Press the monitor Menu button to open the monitor OSD (On Screen Display). The bottom of that screen should show a resolution. What is listed?
1920x1200@60Hz
* Was the monitor purchased directly from Dell or some reseller?
Direct from Dell.

FWIW, I tried to go through the Dell support contact page and was directed to a phone number, the technician that answered the line (name is Hardik) read the standard script, but I told him the issue is showing even without the computer plugged in and that I believe I have an issue warranty covers. He insisted I reboot my system and hit F12. I told him I have a Mac and he told me I need to call Apple Customer Support because they have the 'codes that can be downloaded to make the monitor work' he then proceeded to tell me that they only support Dell Laptops. After asking for a supervisor, he told me that he already to spoke his supervisor and that his supervisor said I needed to contact Apple. I asked to be able to exchange the monitor and he 'warm transferred' me without giving me the number to Dell Customer Care, which apparently was closed. I find the Technical Support & Warranty people who answer the phones extremely lacking in knowledge courtesy.  

Please help