In some cases maybe mod_rewrite module in apache is not loaded . Check your apache configuration.

Update:

Windows xampp : Open xampp/apache/conf/httpd.conf and uncomment mod_rewrite module.
Windows wamp : Open wamp/bin/apache/Apache2.x.x/conf/httpd.conf and uncomment mod_rewrite module.
Ubuntu : Type in terminal : a2enmod rewrite
  Ubuntu manual : cp /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled/rewrite.load
And then reload apache
Ubuntu : service apache2 reload OR service apache2 restart
Windows : From xampp or wamp control panel.

It might be the mod_rewrite module is not loaded.

Windows xampp : Open xampp/apache/conf/httpd.conf and uncomment mod_rewrite module.
Windows wamp : Open wamp/bin/apache/Apache2.x.x/conf/httpd.conf and uncomment mod_rewrite module.
Ubuntu : a2enmod rewrite && service apache2 restart or cp /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled/rewrite.load

Then reload apache

maybe mod_rewrite module in apache is not loaded . check your apache httpd.conf ..

In some cases maybe mod_rewrite module in apache is not loaded . Check your apache configuration.

Update:

Windows xampp : Open xampp/apache/conf/httpd.conf and uncomment mod_rewrite module.
Windows wamp : Open wamp/bin/apache/Apache2.x.x/conf/httpd.conf and uncomment mod_rewrite module.
Ubuntu : Type in terminal : a2enmod rewrite
Ubuntu manual : cp /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled/rewrite.load
And then reload apache
Ubuntu : service apache2 reload OR service apache2 restart
Windows : From xampp or wamp control panel.