I have installed, upgrade and run XOOPS successfully on localhost until I decide to upgrade my db management skill. MySQL was then run as root with no password and now i have installed the password and as a result I cannot accessed the webpage. Try to edit mainfile.php but no success. Need help from the expert, instead of reinstalling xoops.

did you download the mainfile.php from your website, changed the password and reuploaded?

That should be the way to do it. Could you elaborate on "no success"?

I don't understand what do you mean by download. The file is in my local machine and I just access the backend and open it using php editor, but I noticed this file is read only file. I wonder if I have to change the status to read and write as well in order to be able to insert the new password into the mainfile.php. My XOOPS installation is on XP.
The error is: Error [Xoops]: Unable to connect to database in file c:\program files\apache group\apache\htdocs\mysite\class\database\databasefactory.php line 34
Problem solved after describing the problem to you: the write permission problem!
BTW Thank you.

If you just changed the root password for MySQL in your local setup, you might need to 'FLUSH PRIVILEGES' for it to take effect.

If you have phpMyAdmin installed, you can just click on the link given in the index page. Or you can use the MySQL command line.