PLEASE HELP – SITE MISSING after trying to move

Oh Gosh, what have I done??? I have been working on my blog for the past month now, and it was almost finished! I currently have my site at example: http://www.domain.com, I installed the wordpress on http://www.domain.com/blog – I wanted to redesign my site completely, and then just load my wordpress site to http://www.domain.com (and not the http://www.domain.com/blog)… so when I finished with my site I wanted to move it to my main domain… I went under wordpress settings, and changed my website host name from http://www.domain.com/blog to http://www.domain.com – when I entered save, the next moment I got a error message, when I try to log into my wordpress site, I cant do it… also all of a sudden my http://www.domain.com/blog site does not exsist.
PLEASE tell me what I can do to resolve this issue