Please ask your hosting provider to check permissions for you!
You need at bare minimum 444 permission in the public_html directory to view it, although I'd really recommend higher permissions than that. Also look to see if there is a .htaccess file in your forum directory. If there is, look for this line:
Options -Indexes
Change that to
DirectoryIndex index.php
Why did you change topic content and title to "Solved"...? How will that help other people? Please tell me.
Yea, its "mark as solved" not delete entire post contents. What is the point of that?