You might have experience this issue with your Drupal Installation sometimes. Your Drupal Installation shows blank pages as well as user login returns blank page with yoursite.com / node?destination=node link showing 500 or 404 error.
Well its cause when installing a module. So here's the solution for it.
1. Login to PhpMyadmin
2. Select your Drupal Database
3. Select table "system"
4. Then Browse the table. If needed set phpmyadmin to [show] 1000 rows.
5. Edit the entry for the module you last enabled in the table.
6. You see its Status us set to "1" -- Set its Status to "0"
and save.
You are done. Now refresh your site. It should work
