My site Hacked by NsNs 1337

Please help, my site has just been hacked into by a masked guy NsNs 1337 putting his wallpaper to replace my index file. I tried locate the remains but no avail, DB data still intact. I tried a fresh installation, it was not successful telling me that the old directory still exist which is not there?!! could it be hidden, please how can I retrieve.

Thanks.