cant login to 1 of 2 blogs

Hi, i have 2 blogs running on 1 database. Yesterday it was ok, but to day i cannot login to 1 blog ( second 1 login works fine)
i go to http://www.myblog.com/wp-login.php as usually, enter user and pass, press login and get page cannot be displayed 404 error. pass and user are correct. Second blog works ok. Yesterday i logged in both perfectly. Today after doing nothing- cant
Anny suggestions? 🙁