OK, I see what's going on.
The biggest problem is this:
void showBuffer ();
{
blit (buffer, screen, 0, 0, 0, 0, 640, 480);
}
Does not declare a function because of the semicolon after the parenthasis. Remove it in order to define the function. You didn't get an error because this was defined within main(). Once you fix it, the compiler will complain, so move it up above main(). For simplicity's sake you might consider moving your variables (like buffer) above it even further.
Once that is taken care of, you'll see a blue bullet go flying. However, it isn't lined up quite right... but that can be a later topic if you need help with it.
