403 Forbidden error

I am presently in the process of preparing a website http://www.vshiksha.com

Firstly, I created a subdomain http://forums.vshiksha.com . After that, I installed phpbbplus forum software (A MODified version of phpbb) over it. I also made some posts and it was working just fine!

After that, for default website, I decided to install a CMS from http://drupal.org . I installed drupal 5.0. But after its installation, I am unable to access http://forums.vshiksha.com , which is located as a directory in the public_html directory (This is the root of my website, where drupal is installed). It is giving 403 forbidden error. I searched the web for this. Many people are facing similar problems. But no solution has till now worked for me. Presently, I am unable to access forums. I am even unable to access another directory on the same server. I tried removing the .htaccess file, but to no use. I even tried to chmod the forum directory to 777. But that also did not help. Please help me!