Remove index.php from my url

Hi All,
I am having trouble removing the index.php from my website URL. I have tried turning on the web server rewrites and looked at the .htaccess and also cleared cache but keep on getting error 500. The url links appear to have changed, but they are brocken and lead to an error 500 page. Having looked on google, qhite alot of people seem to have the same proble.
I have returned the site back to original url settings with web server rewrites turned off and the sites running normally.
Can somebody put this right for me and remove the index.php from my urls.
Many thanks
Carolina