Preloader help please

Hello all,
So heres my problem.

I have 3 buttons on stage and when you click on them a different image is loaded into a movie clip.

I cant seem to create a preloader animation to display while the image is being loaded.

At the start an image is automatically loaded into the movie clip. I know it should be easy for that one but cant seem to do it. Checked all the tutorials on here and I got nothing.

Thanks for your help in advance. :cowboy: