The problem describe below
I have installed magento on my local system, everything is working fine except that the styles are not loading..
I observed that the problem was due to incorrect style sheet url when the request is being sent (found using net in firebug)..
The request url:http://yourmagento.com/var/www/yourmagento.com/skin/frontend/default/yourskin/css/layout.css
The request url should be:http://yourmagento.com/skin/frontend/default/yourskin/css/layout.css
To solve this problem, you can step by step check following\
1, Make sure the ownership of media and var directories to www-data instead of another unix username and giving those folders full permissions.
2, Set Merge CSS Files to “No” in System Configuration -> Advanced -> Developer -> CSS Settings