There appears to be some issue with the handling of the OneNote cache that Microsoft is aware of. I'm not aware of any actual fix for the problem yet, but there is a fairly simple workaround that isn't painful. What you are going to do is go to the working folder where OneNote keeps its cache, delete or rename the cache folder, then restart OneNote and let it rebuild the cache. Here are the steps:

  1. Exit OneNote
  2. In Explorer, open the folder c:\users\[your username]\AppData\Local\Microsoft\OneNote
    Note: Most likely you will need to turn on view hidden files because AppData is a hidden folder.
  3. Rename the folder "15.0" to "15.0.backup" or something like this, or you can just delete it
  4. Restart OneNote. When OneNote starts you will only see placeholders for your folders. Don't worry, just give it some time and let OneNote build the cache and then you should see everything.
You can find another thread on the topic on the Microsoft Community.