Sites may appear broken when enabling Search Engine Friendly URLs in the Global Configuration of Joomla 1.5.2. Also tested and verified to be true for 1.5.3.
To fix this: Edit configuration.php
Look for default configuration: var $live_site = ''
Change to: var $live_site = '
www.mydomain.com
'
Save and upload your file
Note: Make this change only if you are having a problem with SEF.