It looks like you have the same problem OP and I had.
Do what I did, create an FTP account on your server, if one hasn't already been created automatically, download an FTP client (I heard CuteFTP was pretty good, so I got that), and sync them up so you can play with files on the server through your FTP application.
Then, do what esmi told me, download a fresh version of WordPress v3.0, (Top right, big "DOWNLOAD" button) and use your FTP app to re-upload the
You may run into the same problem I did, where your server has permissions set to
411, meaning it won't allow anyone to overwrite them. In that case, you'll have to use your server's file manager to change permissions to something that's at least
611, of all the files that were not overwritten. Then try to re-upload through FTP. Remember to change each file you modified permissions on back to
411. I'm not completely sure on this, but it's been my experience that having the wrong permissions set on the wrong files could not only screw up your site again, but allow hackers access to it.
e-mail me with any more questions: firstname.lastname@example.org
p.s. i love the beatles, that album being one of my favorites.