Can't Upload Pictures

This probably something very simple, but I don’t do much on our company’s website, run by WordPress, but they want new pictures of our apartments (apartment management company) to be uploaded, replacing some of our older pictures. Anyways, I’m looking at an entry and I click ‘Add an image’ and the pop up box comes up, but when I click ‘Choose files to upload’ …nothing happens. I’ve tried messing with ActiveX settings, updated Flash and Java, tried both in IE9 and Firefox, and I can’t get it to work. I’m at a loss at what to do. Any help would be very much appreciated.