I see an error about tables that don't exist
This is referring to tables in your SQL database (MySQL), and it almost always indicates that you recently updated your version of Open edX. As the Open edX project grows and changes over time, new features are added that require new database tables. You need to create those database tables, even if you're not using those features. To create all the database tables you need, run this:
Then try loading up Open edX again, and see if that works.