404 error on http://test.server/

[eluser]inamdar[/eluser]
any how i am getting 404 error when i refresh my home page
and sometime i got my home page.....
http://test.server/
http://test.server

this is my htacess file

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule .* index.php [L]
</IfModule>