Insert Link button won't work in editor

All of a sudden, over the past week, when I’m editing a page using the visual editor (not HTML text view), the Insert Link button won’t work when I block text or select an image on the page. I click and click and nothing happens. The dialog box where you can enter the destination URL never appears. Does anyone know what’s happening? I’ve never had this difficulty before. The only way I can insert a link is to change the actual HTML code for that anchor text which is tedious.