Webserver authentication
Drush may be the best option. You have a command to uninstall a module :
drush pm-uninstall module-name

Otherwise there is a really tricky and dangerous way to do it :
Go on your database on the "system" table. And search for the line with your module and set the status to 0. After that you may need to clear your cache with the function : drupal_flush_all_caches() (add it to a index.php and remove it after).

The second method is tricky and you should prefer the one with drush. I just explain it if you don't manage to install drush on windows.