Can you share a few more details on what you're getting?
I can check it out for you if you want, just PM me further details.
WHen I've had this happen its been due to my DNS not being resolved to the new NameSErver for my site. IE, I setup a new WP site, shift the Name Server. Hasn't resolved yet..if I manually changed the blog URL in WP admin, it would fail to open the dashboard unless I used the IP address for the site ie (http://123.45.678/~blah/sitename/wp-admin). Once the domain had resolved, www.sitename.com/wp-admin or sitename.com/wp-admin worked no problem.