Thanks for all.
The problem was that I imported all databases from old mysql server, and older user database running in new mysql server (5.5.16) the result is "database corrupt", because mysql_convert_table_format can't repair it.
Be carefull to users that is migrating databases, because this issue is not docummented and I can't locate help using google.
I repair it reinstalling Xampp, importing all my databases (except information_schema, cdcol, mysql and test) and introduced by hand the users (this has served me to make clean). Mysql now is working perfect!