WordPress Security Fix

On one of my websites ([login to view URL]) powered by WordPress there is some sort of infection or virus and I don't know how to remove it. What it does is when I visit [login to view URL] I get a blank screen instead of automatically redirecting me to http://www.mixtapes.tv. On the black page there is this little dot at the top left of the page, it's actually a iframe and every time the page loads the iframe loads a different URL. I've tried all the basic things to fix it such as deactivating and deleting all the plugins, updating WordPress etc. Nothing works. I need this to be fixed ASAP.