Blog disappeared (General Settings corrupted?)

I lost my blog, or rather, when I went to my blog this morning it wasn’t there. All the files are on the server but when I point my browser to:

http://mydomain.com/blog

the error message in Firefox says “Firefox can’t find server at mydomain” and I think the fact is says problem is that WordPress thinks my blog is at:

http://mydomain/blog

without the dot com. And I think this happened because my Internet connecton crashed while I was at this page in WordPress Admin

http://mydomain.com/blog/wp-admin/options-general.php

I had created the blog with the WordPress Address and WordPress URL set to

http://123.321.123.321/blog

and I was in the process of changing them to

http://mydomain.com/blog

I think the database has recorded http://mydomain/blog for these settings.

How can I recover from this? Obviously I can’t run wp-admin at the moment.

Any help MUCH appreciated.

Stephen