After upgrading my machine to Windows 10, I am not happy with what it has done to "Microsoft OneNote". I used to have a lot of notes on this. Now they are nowhere to be seen. It has forced me to waste time setting up a Microsoft "account", but after doing that and starting OneNote within it, the old notes are still lost? Archived? Hidden? Deleted? Does anyone know how I can get them back?
There are 2 possible causes for this.
OneNote usually synchronizes your notes online, using your Microsoft account. Either you have not synchronized your notes before, or you used a different Microsoft account.
In the second case, you should simply use the old Microsoft account to gain access to your notes.
In the first case, if you haven't ever synched the notes they will still be on your disk. The most likely issue is that you are now using a different application, the Windows Store App called "OneNote" instead of the Office Application called "OneNote 2010" (or whatever version you're using). To launch the correct program, click in the search bar on the left side of the task bar on the bottom of your screen, and type "OneNote 20". The search bar should then suggest to launch the correct application - if it doesn't do so instantly, wait for a few seconds.
This is a common issue for Windows 10 upgrades.
Be sure to launch OneNote 2016 (NOT the app called just OneNote) - this version is more likely to contain your old notes. Should this be your solution, you can follow these steps to change your default OneNote version to the 2016 version, as mentioned in this Microsoft support article:
Press the Windows button in the lower-left corner of your screen, and then choose Settings.
In Settings, choose System > Default apps, scroll to the bottom of the list, and choose Set defaults by app.
In the list under Set your default programs, find the version of OneNote that you'd like Windows to use as the default, and then choose Set this program as default. For example, choose OneNote (desktop) if you want to always open notebooks in OneNote 2016.
Click OK to save your changes.