Well, is this just with one project in particular or all projects? If it's just one project, or something you could check in general, is if the Mute button is selected on the far left hand side of the video track in timeline edit mode. If Mute is selected, then the video wouldn't display but the audio would still be present.
Otherwise, if this is more of a general problem when importing all video into the program, you could try another video mode- press "P" on your keyboard to open the Program Settings. Under the Display options tab, under Playback in arranger, try all the different video modes to see if one works for you.
If that doesn't help - what version of Movie Edit Pro do you have and what file type are you importing?