Base Layer Not Showing ... bug?

I've run into the problem that some people have mentioned here, which is that something triggered slide layers to not show the base layer, even though the Hide Objects on Base Layer is NOT enabled. It looks like there is a white box covering the screen and the base layer won't show. Has anyone found a workaround to this, other than starting over? It seems as though the whole file is corrupt as new slides (with new layers) act the same way.

Thanks.