One of the things I've noticed when dealing with mp3 is that sometimes a file(mp3) can be finicky about its player depending on where and how the file was obtained.
a quick fix to any problems you may have when trying to play mp3's is to first attempt to play it with "Soundapp". what this software does is it try's to play just about anything you put in it. If your mp3 is actually an mp3 soundapp will definetly let you know.
Soundapp is available at www-cs-students.stanford.edu/~franke/SoundApp or from
www.download.com
Second Fix:
make sure that your mp3 isn't in a zipped format. just drag your file onto your stuffit expander icon and see what happens. either you'll get a message saying that "this file is not a valid format" or you'll unzip you file.
I bring this up because you said that the file was "sent" from another comp, which means some sort of compressing could have been involved.