Contrast levels won't stick

I'm using CS3, and having a problem whenever I go to Image>Adjustments> Levels, or Curves, or Brightness/Contrast.
The adjustments look fine in the preview, but when I click OK, the image snaps back to what it was before, unchanged.
When the the zoom is on a one-to-one ratio, even the preview won't show any changes. I also tried to use Layer> New Layer Adjustment> etc., and the adjustments would stick. But If I tried to flatten the image or otherwise make the changes permanent, again the adjustments disappear leaving me with the unchanged image.
I reset the settings back to default thinking that I might have unwittingly changed something, but the problem still persists.
I'd appreciate any help on this matter, it's frustrating!

Are you viewing the file at 100%

Suggestions:
Make sure the mode settings and color spaces are set correctly. Are you opening files that are flagged as "read only"?

Yes, I went to view>Actual Pixels. When I am working with the contrast at 100% zoom, even the preview button will not show any change. At levels other than 100%, however, the preview does work.
There is no zoom that will enact the change after I click OK, however.

I am having exact same problem. Checking the "Use Legacy" checkbox doesn't correct the problem for me. I can see my changes in the preview, but when I click "OK," it snaps back to the same image as before I started. Very frustrating! Anybody have an idea how to correct this issue?