This post straight from the “Do As I Say, Not As I Do Hall of Shame.”
Changing themes in WordPress is so easy. Simply install the theme, activate it, and voila! You’ve changed the look of your site.
But before you hit that “activate” link, there’s one very important thing you should do: deactivate your plugins. Your current theme may use certain plugins that conflict with the new theme you want to use. If you don’t deactivate the current plugins, when you activate the new theme, your site may completely disappear. You won’t see your login page or your admin panel or anything. If this happens, don’t panic. What you need to do is connect to your site and delete the offending plugin(s).
You can connect to your site using FTP or through an interface offered by your web hosting company. Find the proper directory — all plugins are located in the following WordPress directory: wp-content/plugins — and delete the plugin. If you’re unsure of how to do this, or do not know how to connect to your site, contact your web hosting company and see if they can help. You can also ask for help in the WordPress forums.
Finally, if all else fails, restore your site using the back-ups you made of your database and files. This assumes, of course, that you’ve backed-up your site. You have, haven’t you?


