OneNote 2013 microphone (mic) not working - Microphone Muted intermittently

If OneNote 2013 is not recording consistently (i.e., inconsistently recording or OneNote 2013 recording is just not working) on your Surface Pro 3 (mine is 256GB with OneNote 2013 Retail (Academic) version), then you're not alone (see this post at Microsoft: http://answers.microsoft.com/en-us/office/forum/office_onenote-onenote_2...).

I had this problem too while I was studying in Paris. I recorded audio from class lectures Monday through Friday at least once per day and, for one week, LOST (actually never recorded) the audio for 60% of my lectures. Things worked fine before the firmware updates (August 2014-May 2015) and then the microphone started muting randomly. This was my solution:

Preliminary:
Make sure that OneNote 2013 the DESKTOP version (not the APP version) is set as default: OneNote 2013 -> File -> Options -> Advanced -> Make OneNote 2013 (desktop) the default OneNote application...

Make sure you've got the latest Office updates (not just the Windows ones). Click Windows button -> type Windows Updates -> Change Settings -> Give me updates for other Microsoft products when I update Windows.

Just prior to recording:
1. Open OneNote, start recording, wait 2 seconds, then click stop
2. Right-click Volume icon -> Recording devices -> double-click Microphone -> Levels -> ensure microphone is NOT muted (it frequently mutes just after recording)
3. Repeat #1 and listen to its playback.

If it works, record your lecture. If not, repeat #1-#3.