Just go to the directory:
Edit the following files :
Then restart the services of HP from the Services mmc console of windows (particularly the HP Insight Foundation Agent service)
Then try to open the manage homepage again. You should be able to access the site. Your browser will use the ADMINISTRATOR access by default.
Just dont forget that as soon as you are logged in change the password and revert the changes that you have made to the mentioned files. And restart the services again to ensure that youll restore the security settings.
Hope this helps.