Split the movement of your actor in the horizontal and vertical axes. Then, when checking for an intersection with a wall, you also check both directions separately. When it happens while moving horizontally, you reverse the horizontal movement (multiplying by -1) and when it happens while moving vertically, you reverse the vertical movement.

The code would highly depend on how your actor moves. Show current code of actor you want to bounce off edges. If you are not too worried about the code itself and just want to get that behavior working, I have a QActor class ("Q" for "quality") you can extend that would do the trick. If you move by rotation, you would use something like the following: -- if the actor is to remain upright (no rotating of actor), then something like this: The QActor class can be found in my Asteroids w/Improved QActor class scenario.