The password in the file was different from the one in dbispconfig, changed it in the file because I've tried to change the mysql password to admin before (is this the right way to go?).
You seem to mix up things here. The password in the file is the mysql password for the ispconfig mysql user. It is not the admin password for the ispconfig controlpanel login, so this password is not the same then the admin password.
Have you made a backup of the file so that you can restore the original file?