installed drupal site locally but not working (XAMPP)
One reason for this can be 'the apache server's rewrite mod is not enabled'.

See if 


  localhost/sitename/index.php?q=user/login


is working.

If that is working then try enabling Clean URL (sudo a2enmod rewrite for LAMP).

Few links that can be related to the problems.

http://drupal.org/node/1186762

http://drupal.org/node/333675