I am using WMM 2012 version 16.4.3528.0332 with Windows 7.

I have been editing a video over the past few days in WMM. I'm using MP4 files. Everything (audio and video) has been working fine, though I have lost all sound a few times in WMM while in the middle of editing functions, but have been able to restore the sound by closing and restarting WMM. Now I have suddenly lost all sound (including original video audio as well as music tracks I have added that previously worked fine) and restarting the program does not restore any sound to the video project.

All other sound on the PC works fine, such as Windows Media Player, ITunes, etc. The disappearance of all audio is only occurring in WMM. The music files I have added to the video project, as well the audio indicators on the original video clips are showing up on the video timeline just as they did when I had full audio on the project. I have checked all audio and music volume controls in the WMM program and on the PC itself and nothing has changed to cause the loss of all project audio.

How do I restore the audio to WMM so I can complete my editing project?