[PD-John]

First, check that the playback engine is set to the Mbox (Setup > Playback Engine). Then create a mono audio track and set the input to the input you've plugged your mic into on the Mbox. Turn up the gain knob on the Mbox for that input and click the record-arm button on the audio track in Pro Tools. You should be seeing some level as you speak into the mic - try to set it so it's just into the yellow part of the meter. Then press the record button at the top of the Edit window, then hit play to begin recording. Once you're done recording, turn off record-arm on the audio track and press play.