Sometimes when upgrading to a new version of WordPress (WordPress 3.0 is out today by the way) it can cause your site to break. This is usually caused by one or more plugins being incompatible with the new version. To fix it, follow these simple steps:
- Connect to the server via ftp or ssh
- Rename /wp-content/plugins/ to /wp-content/plugins-tmp/
- Try to go to the site. If the site comes up, continue. If not, its probably the theme that is incompatible and will take some further debugging.
- Go to the plugins page in the admin. This should automatically disable all plugins.
- Rename /wp-content/plugins-tmp/ back to /wp-content/plugins/
- Activate one plugin at a time until the site breaks again to figure out which plugin is causing the problem.
- Repeat steps 1 – 6, but skip the plugin that broke the site.
- Look for available updates or alternatives to the broken plugin.