Can we see the coding? Also, if your actor is only one color, you may have accidentally pressed the "choose color to be the transparent color" when creating the actor, making it invisible.
The easiest potential solution is just to delete the actor and put it back in again. Is that much of an issue?
Since you don't want to screenshot your code, it makes it very hard to help you. Here is my final suggestion to you: use a different graphic that you already know works and attach the behavior to it. If the actor disappears, you know it is the behavior; else, it is the actor.