I figured out my problem, My python script had the line below:
os.system('mpg123 -q Memo.mp3 &')
This code worked great from a command line while I was logged in as"pi", but when the script is run on boot from /etc/rc.local, the file takes on root's environment variables, and the Memo.mp3 file which is located in a folder under pi's home folders is not found. When I run from a command promptas pi user, the foldersunder pi's home directory are in the pi user's PATH. Therefore, the script runs fine since the file is found.
I want to thank the soapBAR2's post which led me to my solution: http://ubuntuforums.org/showthread.php?t=1313921
When I changed my code to add the full path to my mp3 file, as shown below, the mp3file plays on R-Pi boot up. I changed the code as shown below:
os.system('mpg123 -q /home/pi/Desktop/Current_software/good/Memo.mp3 &')
I hope this helps someone else with this problem. I incorrectly thought my problem was a monitor setting which was a red herring.