When legitimate pop-ups are being blocked, there are a couple of things to check.
First, click the AdBlock button in the browser toolbar and select Pause on this site, then reload the page. If the pop-up opens, the culprit is one of your filter lists. Usually it's Fanboy's Annoyances, which specifically blocks pop-ups that aren't ads but may still be annoying. If you have subscribed to that filter list and you find it's blocking a lot of pop-ups you want to see, then we recommend unsubscribing from it.
If pausing AdBlock doesn't allow the pop-ups, then there's something else blocking them. Most often it's your browser's built-in pop-up blocker. If that's the case you'll see a little icon in the address bar. Click the icon and a dialog box should open where you can allow pop-ups on that site.
If you don't see that icon, open your browser's extensions page. Look for extensions that block things like pop-ups and disable any you find.