Yosemite not able to use external display at full resolution I had problems with Mavericks in getting full resolution in my monitor Dell U2713H (connected to a Mac Book Pro). I used this solution from this site to fix the problem:

I downloaded the file from http://embdev.net/attachment/167830/U2713H_U2713HM_Mac_EDID_override.zip, 
and after copying it to /System/Library/Displays/Overrides and rebooting, my display was showing again its awesome full resolution. 

I did it again when I installed Yosemite but it does not work. Any idea to fix this problem for Yosemite?. Otherwise I will downgrade to Mavericks again. Thanks!!
Upgraded to Yosemite 2011 13" Macbook pro.  Display port to VGA is what I used with Mavericks.  As soon as I updated to Yosemite my macbook would not recognize my external display.  Applecare support were stumped.  Got a Display port to HDMI adapter 3rd party, and voila back in business.  Yosemite does not like display port to VGA adapters.  I tried apple branded VGA adapter and nothing.  As soon as I switched to HDMI all resolutions appeared.