Site links wrong, Login button redirects incorrectly.

My site was fine until I accidentally changed (I think) the defaults page.
I think I changed the web address of the blog somehow. When I go to the blog, it has no theme. If I try to get to the admin pages I can go to:
http://mysite/blog/wd-admin and get the login prompt page. The SOURCE for that page has the wrong address for the POST function of the “Login” button, so I can never login. It is missing the “/blog/” in the link and posts to a non-existent page. What file can I edit to correct the link, or is it only in the database? If so, is there any way to fix it?
Please assist.
Thank you in advance!