upload media via wp using mamp

I’ve installed MAMP to learn WP custom themes on my localhost. Everything works fine until I attempt to add a header or a background image.

I browse for the image and select it, window above goes blank. When I click upload I’m directed to the Page that is labeled Crop Header Image. It is completely white but the outline of the crop box and the Crop and Publish button is all there. When I click that Crop and Publish button it goes back to the Custom Header page with the view window totally blank.

I checked to see if the folders were created, uploads > 2011 > 04, and they were all there with the images in them and everything.

The same thing happens with the custom background setting.
Also, nothing happens when I try to load a Featured image.

PLEASE HELP!