HELP!!! The topics won't open!!!

On the forum, go to the control panel (it's next to the site map). Then: options, and scroll down a bit; you'll find:

Here, you can select one of the thread display options. For a detailed description of each option, see this help page. Using this option, you can select the number of posts to be displayed on one page. You can define the period of time for which threads will be displayed. Threads older than the period you specify will not be displayed.

it should look like this:
1) Linear
2) As in settings
3) As in settings