Fixed the camera - I think.
I finished replacing the LCD screen on my Canon SD550, following Chris Hutchcroft's directions.
His Step 11:
If you have screws left over you've done something wrong. Curse, disassemble, and find where the screw came from. The last thing you want is loose camera innards.
Well, I have an extra screw - and a 3-sided white rectangular frame. Oops.
I remember a screw loose (in the camera - quit laughing) when I opened it up, but for the life of me I cannot determine how to get the frame back in. It came out from between the LCD screen and the backlight.
I buttoned the camera back up, and it works correctly, so we shall see.