Almost sounds like you were hacked. Unfortunatley this is a good example of why you should backup your site and database often. I would change your admin/user, and datebase passwords, then you could use the blocks section of the install sql to restore your block info. If uploading a new index didn't solve the redirect problem then they hid it somewhere, search your database for the sitename it's trying to redirect to.

I haven't looked at Platinum since Tech stopped working on it, does it come with Sentinal? If not, install it right away.