Hi Katie,
Sorry you’re still having trouble, and I only noticed this response now.
You can also try talking to your host and having them check your account, and error logs.
Did you try asking your host to check the error logs? Error logs are also often viewable in your own control panels, for example cPanel offers an error log. The error logs show recent 404 and other server errors, and may provide clues about the source of the error.
Another idea is to temporarily switch to one of the default themes (like Twenty Eleven) to see if the problem persists. If the problem goes away, it means it’s a theme problem, in which case you’ll need to get help directly via Thesis, since it’s a commercial theme. Note that you may have to reset some of your theme settings when you switch back to Thesis, so be sure make a careful note of them. (i.e. custom header, widgets, possible other things. I have never used Thesis so I don’t know what settings may be affected.)
Other things to try:
– reinstall WordPress – replace the WP files in the root, as well as wp-includes and wp-admin, with a freshly downloaded copy, assuming you’re running 3.3.1. Do not touch the the wp-content folder, .htaccess and any other files you may have modified. Always make backups of everything first! More info here: https://codex.www.ads-software.com/Updating_WordPress#Step_1:_Replace_WordPress_files
– do a database repair – best to have someone familiar with phpMyAdmin do this for you as it needs to be done carefully. Be sure to make a backup of your database first.
– hire a WordPress expert to take a more hands-on look at the issue
– start over with a completely fresh installation of WordPress and fresh database and import your posts
Don’t despair – there are always more things to try. Good luck!