Irritating White Screen in Viewer

Hello, all

I have a new problem which I'd love some help to address. One day last week when I fired up my Mac to start editing in FCP 7, the Viewer showed up white. When I hit "play," everything works. But when I pause or stop, it's white screen all over again. Nothing else is affected. Rebooting didn't help. Here, six or so days later, no change.

What do I need to look at to fix this?

Thanks very much,

-- Bill