See also the following thread:
It's most likely a problem with your X Windows (your graphical system). Booting into single-user
mode (ie only text/terminal, no graphics) and then reconfiguring your graphical settings should do the trick.
The gmd.pid file is typically a file that stores the Process ID (a number that indicates a specific program) of the "gmd" program (probably related to your X Windows/graphics somehow). If the .pid file exists, then your system "knows" that the gmd program is running and knows it's PID. Programs started automatically at each boot,
such as the scripts in /etc/init.d and most daemons/services that are running, use this pid-file mechanism.
The warning simply sais that:
-the pid file was found, so the "gdm" program should be running
-but it isn't running, so it was "murdered mysteriously" (not to be taken literally). When you stop a prograp, you can use the "kill" command. A program that is stopped in such an abrupt way is said to have been "killed".
Normally, only the users who launched the program and the root user can kill programs.
The term "murdered" here simply implies that someone unknown has "killed" (stopped) the program.