2.8.4 strange behaviour on login

hello,
I have installed 2.7.1 spanish version, I configured all the blog with this versions and then updated to 2.8.4.
During cookies were up to date I could work perfectly on wp 2.8.4 and it seems that installation were ok.

Now I’m trying to access through an other computer and could not log into wordpress as admin.

I tryied to reset password using phpmyadmin (enconding my password as md5) and on trying to login the page simply not redirect to main page. If I put a bad password wp says me that password is bad if I put it ok, wp don’t says anything and gives me again to login page.

Wich tests I could do more? there’s some way to enter without password? I have to leave modified the site as soon possible (to much work!)

Thanks you much guys o/