I’ve only been using Daz for a short time, but I thought I’d add my input if it helps. I’ve discovered Daz generally displays content appropriate for the item you have selected, for example clothing materials if you have a dress selected, or skin if it’s a character. The first thing to do is ensure you’re selecting the correct model if you don’t immediately see your content, which you can do using the scene panel (by default this will be on the right-hand pane).
Also, as mentioned by Szark content tends to install metadata which is initialized when you run Daz. A window should pop up detailing the new content and then it will add the necessary information. Not all content does this though, so you might have to check your Content Library to find some items.
Other than that the only thing I can suggest you check is that the install directory matches that used by Daz. It’s a silly thing, but generally some of the most frustrating problems have the simplest answers. If you still get problems, post back with extra information such as what you’re trying to install and where and we might be able to help you further. Good luck.