1.Download wp-config.php (if you don't have shell access).
2.Open it in your favorite text editor.
3.Check that the first line contains nothing but <?php, and that there is no text before it (not even whitespace).
4.Check that the last line contains nothing but ?>, and that there is no text after it (not even whitespace).
5.If your text editor saves as Unicode, make sure it adds no byte order mark (BOM). Most Unicode-enabled text editors do not inform the user whether it adds a BOM to files; if so, try using a different text editor.
6.Save the file, upload it again if necessary, and reload the page in your browser.