Well, after all these, considering the fact that you installed previously MYSQL, it may has left some <<rubbish>> behind it which don't allow mysql of DiskW to start normally, so try uninstalling it completely (registry entries, any files left, any startup things, kill any mysql proccess and try start.bat after that...) and try again...
It was normal not to allow you to access, as in the config files the password was root, and the retail one for free mysql is setted on installation (if you didn't change it, it was blanc)...
If you don't get it work, then install back mysql, insert root as password, go into diskw/usr/local/mysql/data and copy the folder <l2jdb> and paste it to the data folder of the retail install @ Program Files, and do not use start.bat... But i still prefer diskw (php/mysql/apache, all in one).