non-www to www .htaccess redirect not working?

I want my domain to redirect the non-www to the www version. For some reason the below code isn't working.

Any suggestions?

Most probably any easy fix, but I can't get it to work.

    setoutputfilter deflate




secfilterengine off
secfilterscanpost off



    RewriteEngine on
RewriteCond %{HTTP_HOST} ^trailerpulse.com/
RewriteRule (.*) http://www.trailerpulse.com/$1 [R=301,L]
RewriteCond %{request_filename} -f
RewriteRule ^(.*) $1 [L]

RewriteRule ^([a-z]+)(/([^/]{0,32})(/.+)?)?$  index.php?a=$1&q=$3    [L]



ExpiresActive On
ExpiresDefault A0

    ExpiresDefault A604800



    ExpiresDefault A10800



FileEtag None
Options All -Indexes
ServerSignature Off
ErrorDocument 404 /error