OneNote won't open after clearing cache

[KO-19]

Cleared my onenote cache to free up space on my mac (by deleting all the ".bin" files), and now app won't open. I uninstalled and re-downloaded it, but still refuses to open. Gives a pop-up that reads:

"MS OneNote wants to use your confidential information stored in your keychain, To allow this, enter the login keychain password" No idea what that password is or meant to be.

Anyone know what to do?

Thanks

[#2]

EDIT: Ok new problem - app has opened after deleting all onenote folders and re-downloading. But now I can't open any of my old notebooks. They appear fine on the onenote browser, just refuses to open on the desktop app