This same thing happened to me… Everyone told me to shake it and leave it in the sun. Don’t do that! That will make it too hot. Instead, leave it facing down in a dark, room temp room and it should develop. If still not working and it’s the first pic in that film cartridge, it might be because the company buts a black starter to make sure your camera is working properly. If it is the first pic and the tester doesn’t come out, than you might have to open the back of your camera (where you place the film) take out the film (if you have in already) and you shall see a little rectangle. If the rectangle is dirty, simply add some baby oil on a Cotten ball and wipe the rectangle gentally . Please comment if none of this works and I’ll do some research.