Nesting pages won't show on Navigation Menu

I am super new to wordpress..Definitely a novice but learning. Am using D5 Discussion theme (free) and the nesting pages were fine–when i hover over parent tab on the navigation bar, the nesting pages would pop up. I installed Form Maker plug-in and after that it stopped working. I uninstalled and re-installed both to see if that worked, but it didnt. Someone please give me a clue. i tried activating a few different themes and some of them will show nesting pages, and some won’t. I really like this theme that I’m using, but have no clue what the issue could be since it was working fine just yesterday.