I've been hacked!

I’ve been trying to research this hack on my own to no avail. Can anyone help? Someone hacked the site and changed the name to hwins2005. For awhile it would only display: “this site has been hacked by hwins2005”.

When I tried to look it up on google there were just a ton of other sites that had been hacked and had their URLs changed. Because the URLs were changed to that, when I searched for a solution I just got pages of other sites that had the same problem.

In addition to that, I cannot access my admin page. Help please!