At the moment I cant log in, it tells me their is an internal server error.
Without the text of the error message, there is not an awful lot to go by...
Try these steps (which mostly I copied from another posting).
Backup all of your files and database and put that backup somewhere safe.
http://codex.wordpress.org/WordPress_Backups
http://codex.wordpress.org/Backing_Up_Your_Database
http://codex.wordpress.org/Restoring_Your_Database_From_Backup
Download the latest version 2.8.4 from here.
http://wordpress.org/download/
After you have backed up your files, extract the WordPress files and overwrite your existing files. This will only wipe out the core files and not your themes or plugins. If you have modified any files from the WordPress distribution then this will overwrite those files too.
Move any .htaccess you have to somewhere else not in your webserver's directories. Insert into a blank .htaccess this text and save the file.
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
If that still does not work it might be a plugin so go to your wp-content directory and rename plugins to plugins-old.
You might want to try renaming the plugin directory first.
If something goes really spectacularly bad, just restore your file and database backup and you'll be right back at square one.