What dropdown menu do you mean?
Where is menu?
Hi. After installation and login to admin, i dont see menu and see many <p> tags. What is this?
Looks like your installation was not successful.
Could you try rebuilding NodeBB? Perhaps something happend with just this step and redoing it will fix the forum.
If this doesn't work, then reinstallation will probably be required (or at least the easiest way).