there is a difference between recording in stereo and playing back in stereo.
you should ALWAYS be playing back in stereo...but not necessarily always recording in stereo.
stereo means two. two speakers or two microphones. when you press play the sound comes out in stereo...two speakers. But when you record a voice, you record with one microphone...making a mono track.
for some reason, in PT you're not doing it right. It sounds like to me you're probably creating a stereo track in Pro Tools when trying to record your voice. What's happening is Pro Tools is looking for a stereo source (remember...stereo=two, so PT is looking for two microphones). But you're using one! So you're probably setting the stereo track to Inputs 1/2, right? But you have a microphone only in channel one, right? So you're hearing only the left channel (channel one....channel two is recording blank).
What you NEED to do is create a MONO track and set it's input to channel one. Making sure the pan slider is in the middle....record now, and provided the output of the track is Output 1/2, and your headphones are properly plugged into the Mbox's headphone jack....you should hear in stereo now.
double check that you have a mono track.
File-->New Track-->Add mono
Input set to Channel 1
Output set to channel 1-2
If all that is correct...it's either something wrong with your I/O setup or the headphones you're using.
-----edit-----
Glen beat me to it! I was typing like crazy to beat him
