Enable rewrite in your HTACESS file, like this:
<IfModule mod_rewrite.c>
############################################
## enable rewrites
Options +FollowSymLinks
RewriteEngine on
############################################
## you can put here your magento root folder
## path relative to web root
#RewriteBase /magento/
############################################
## uncomment next line to enable light API calls processing
# RewriteRule ^api/([a-z][0-9a-z_]+)/?$ api.php?type=$1 [QSA,L]
############################################
## rewrite API2 calls to api.php (by now it is REST only)
RewriteRule ^api/rest api.php?type=rest [QSA,L]
############################################
## workaround for HTTP authorization
## in CGI environment
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
############################################
## TRACE and TRACK HTTP methods disabled to prevent XSS attacks
RewriteCond %{REQUEST_METHOD} ^TRAC[EK]
RewriteRule .* - [L,R=405]
############################################
## redirect for mobile user agents
#RewriteCond %{REQUEST_URI} !^/mobiledirectoryhere/.*$
#RewriteCond %{HTTP_USER_AGENT} "android|blackberry|ipad|iphone|ipod|iemobile|opera mobile|palmos|webos|googlebot-mobile" [NC]
#RewriteRule ^(.*)$ /mobiledirectoryhere/ [L,R=302]
############################################
## always send 404 on missing files in these folders
RewriteCond %{REQUEST_URI} !^/(media|skin|js)/
############################################
## never rewrite for existing files, directories and links
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l
############################################
## rewrite everything else to index.php
RewriteRule .* index.php [L]
</IfModule>