I'm sorry to hear about this!
Can you try manually resetting your plugins? If that resolves the issue, reactivate each one individually until you find the cause.
If that does not resolve the issue, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the Twenty Ten theme (WordPress 3.0 and 3.1) or the Twenty Eleven theme (WordPress 3.2 or higher) to activate and hopefully rule-out a theme-specific issue.
And, if that fails to resolve the issue, try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don't forget to delete the original files before replacing them.
If that doesn't work, please contact the WordPress.org Support Forums.