I have been unable to access both my website and my login page. What's going on?
Sounds like your database was updated but your filesystem was not - that could happen perhaps if the development version and the live version share the same database, and only the development version ran the update.
To fix it try renaming the craft/app folder to craft/app-old, then copy the craft/app folder from the latest Craft download into your site.
Backup your stuff first.
Looking through the code this is what you are running into:
Returns whether the uploaded DB schema is equal to or greater than the installed schema
To me that says your database is out of sync. Were you updating to a different version? Perhaps you made the changes locally, then pushed them up but haven't updated your (production) database to reflect the change?