thanks guys for your help....
I was trying tho follow these tips... but it doesn't fix my problem...
Ok, there are two wordpress instalation.. they are the my oficial portal and the development copy (the 'dev') where I used to make changes before to update the portal. They was wp 2.7 but I wanted to update to 2.8.4, then I update files in dev, following steps in http://codex.wordpress.org/Installing_WordPress.
So, I was testing register new user.. it showed a message to check my email box, but I not receive the message (I tried use more email accounts). I also tested the 'lost password' and it showed that message.
I guess it is not a problem with my host because it was working before the upgrade, and it IS working now in portal (wp 2.7), then the plugins couldn't help me because they worked well in portal and not in dev.
I was thinking if wp changed only the files when I did the upgrade. Perhaps wp make changes in other configs when run the new files.. or the error can be a conflict with some info in database ...
any ideia?