Screen is black but, I can still make it work (sometimes)

When I turn on my SX100IS everything seems fine except that the screen is black. I get the Canon start screen. All the icons appears. I can go into menus. Change settings. All seems fine.

If I push the shutter button is takes a picture. The picture is just black.

But here's the kicker. After taking this black picture, the screen is fine again. For a while. I can take a picture or two and then it's back to black. Or if I turn the camera off and then back on, it's back to black. Seems like maybe something is getting stuck?

Also it seems like it's taking a long time for the pictures to be saved when it does work.

Can you help me out, please?