For drupal it s a very common issue that give 500 Internal Server error or 404 Page not found error and for most cases this will be a problem in the Drupal default htaccess file. By replacing or add a new htaccess file will be eliminate most drupal problems. You can download or copy the blow drupal default htaccess file.
You have to unzip this file and put it in to your root folder
You can Download Drupal default htaccess file by clicking below link.