On a rolling release, like Manjaro, it might be better to reinstall from the latest ISO.
A Manjaro user should really review the Stable Update Announcements for each update, at a minimum the first post that describes what changes, any known issues, and any manual intervention.
Any .pacnew files should be reviewed before rebooting.
Search this forum for the error messages, especially solved topics. It might give you an idea what to focus on.
Use root.
If you forgot the password, follow I forgot my password - #4 by Mirdarthos.