BuddyPress.org

Delete the theme that you activated from the theme directory. If that’s what caused the error, then deleting it should revert to a different theme.

If that doesn’t work, you can rename the buddypress plugin folder (which essentially disables it) so that you’ll be back to square one before you enabled BP.

Not sure what caused this. I want to say it’s the theme, but not sure since you said the admin pages don’t load either.