i'm sorry if this exact problem has already been discussed. i tried to search the forums for it but did not come up with anything exactly like this right away.
i usually login to my account via wp-admin. a few days ago, something strange happened. in the middle of writing an entry, the section that shows my autosave status suddenly popped up with a login window. thankfully, i quickly copied my unsaved text and pasted it into an e-mail to myself. then, i reloaded wp-admin. i had my usual wp-login.php screen. i tried to login with the correct username and password but ended up back at the wp-login.php. i tried the admin username. still the same thing. i tried purposely mistyping the password. only then did i get an actual "ERROR: Incorrect password." message. when i use the correct passwords for the correct usernames, i just end up back at the wp-login.php screen; over and over.
i tried clearing my cookies. i tried restarting my browser. i tried uploading a new copy of wp-login.php (from wordpress 2.6) to the directory. i tried adding the line "@define(’ADMIN_COOKIE_PATH’, ‘/’);" to my wp-config.php file.
i don't get what's happening.