When submitting the form site.com/blog/wp-admin it goes to site.com/wp-admin

When submitting the form site.com/blog/wp-admin it goes to site.com/wp-admin

I have 2 wordpress websites. One at site.com and the other at site.com/blog.
I want to go to administration of site.com/blog, but when I point to site.com/blog/wp-login.php or site.com/blog/wp-admin/ and login, it goes to site.com/wp-login!!!! (Both wordpresses have the same user/passwords)
Please help me stay at when I point the browser to!