1. Start up the computer in single-user mode.
# -s
2. This step contains a series of commands, each preceded by the pound sign (#). You should type each, pressing Return after each to execute it before continuing to the next.
# fsck -y
Note: If the result of this file system check is: "***** FILE SYSTEM WAS MODIFIED *****" then repeat fsck -y until the result is "** The volume xxxx appears to be OK", Where "xxxx" is the name of the computer's startup volume.
#mount -uw /
#rm /Library/Preferences/com.apple.windowserver.plist
#cd /Users/username/Library/Preferences/ByHost
#ls
Note: Using the ls command here lists all the visible files and folders in the ByHost folder. Locate the file named "com.apple.windowserver.xxxx.plist", where "xxxx" is an alpha numeric string.
# rm com.apple.windowserver.xxxx.plist
Note: In place of "com.apple.windowserver.xxxx.plist", use the file name you located in the last step. This step deletes the file located in the last step.
# reboot