Something has gone seriously wrong with your blog. You may have recently updated to the latest version of WordPress, upgraded, or installed, a new plugin or switched themes.
How do you start to track down and fix the problem?
1. Plugin Issues
Plugins are the most common cause of WordPress problems. Especially if you’ve recently upgraded to WordPress 2.8 or installed some new plugins.
Deactivate all of your plugins to see if this resolves the problem. Yes – we know that you can’t live without every single one of your plugins. But what do you want? Lots of essentially useless plugins or a working blog?
If the mass plugin deactivation resolves your problem, re-activate the plugins one by one – checking the site thoroughly after each re-activation. Eventually you will find the problematic plugin(s) – at which point it will be time to look for a compatible replacement.
If a mass plugin deactivation didn’t work or the problems are so severe that you can’t even access your Dashboard, try resetting the plugins folder via FTP or phpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems. If you can manage the phpMyAdmin approach, use it. Experience suggests that it offers the best success rate in eliminating problematic plugins.
2. Theme Issues
The more feature-rich the theme, the more likely it is that one or more of the features can cause problems elsewhere.
Switch to the default theme to rule out any theme-related problems.
If the problems are so severe that you can’t even access your Dashboard – let alone change themes, rename your current theme’s folder using FTP. You'll find it in wp-content/themes/theme_name. If in doubt, rename all theme folders except default and classic.
Your blog should automatically switch to the default theme. If this resolves your problem, then it was theme-specific. Delete your old theme and find a new one.
3. Permalink Problems
If your Page, Post or Category links are all broken, reset your custom permalinks back to the default setting via Settings – Permalinks. If this works, then it’s likely that you mis-configured your permalinks. Ensure that you understand how to set up custom permalinks before trying again.
4. Known Browser Issues
If you’re using Firefox 3 and have Google Gears installed, deactivate/delete this add-on. It’s not compatible with Firefox 3 and can cause problems in WordPress.
5. Research The Problem
Search the WordPress forums. Don’t just post a question without checking to see if it’s been answered before. The forums are extremely busy and no-one is being paid to help, or answer, you. Do some of your own research first.