My external display is not working since I upgraded to 10.8
I have a mid-2009 MBP connected to a Samsung SyncMaster 915N by VGA, and it no long works correctly after upgrading to Mountain Lion. Specifically, after I upgraded, the next time I connected to my external monitor the display would go in and out (I.e. every few seconds the display would toggle between showing my desktop and black screen). Also, when the desktop was visible I observed horizontal flashing lines.
I found a workaround by changing from full resolution (1280x1024) to a lower resolution (1024x768), but obviously this is not optimal. Changing the refresh rate at full res did not solve the problem.
MacBook Pro, OS X Mountain Lion