Thanks so much for your suggestion! I did not know about this other forum.
I was able to find the answer!
I am quite embarrassed
as to how simple the answer was, but I will share it with everyone in hopes that it will help others out with the same problem.
In addition to the SOFTWARE audio control, my laptop also has a small HARDWARE audio control. It is a small wheel on the side of the laptop. I must have unknowingly brushed against the wheel and turned the volume down as far as it would go!
All I had to do was turn the wheel back up!
BTW, here's the link that that had the answer: http://notebookforums.com/showthread.php?t=79032
Thanks again for the suggestion, Koan!