5
xoops_config table for your default theme
xoops_users table for your usid, you should be number one if you were the one that installed xoops.
You click on the table and then click browse on the tab at the top of your phpMyadmin page. Then you would click on edit by your usid. With the xoops_config table you would also click browse and where it says default theme, just change the name to one of themes that do work right.
If you have your site hosted and they provide phpmyadmin, then that is what you use to work with your XOOPS database.