Hi

I am having a similar problem with MEP MX at the moment - importing video files does not always import the sound correctly. 

Try this:-

With MEP open press the Y key to open the program settings dialog. 

On the Folders tab make a note of the location of the Import folder - it should say AudioTemp at the end.

Close MEP

Open My Computer (Windows XP) or Computer (Vista and Windows 7) and navigate to the folder you noted above. 

In the folder you should see some wav files with the same name as the video clips in the project  - delete them all.

Start MEP and open the project again - you should now get the sound back.

HTH

John