Sounds like you might have a corrupted preview cache. Try this: http://members.lightroomqueen.com/index.php?/Knowledgebase/Article/View/1140/188/lightroom -says-my-preview-cache-is-corruptedhow-do-i-fix-it
So even when you went to Library menu > Previews > Render Standard Sized previews, they didn't rebuild? Behaviour remained exactly the same as before?
If so, you can trash the newly created preview cache and rename the old previews cache back to its previous name to put them back then.
Next in line, monitor profile, although I'd expect that to affect Develop too. http://members.lightroomqueen.com/index.php?/Knowledgebase/Article/View/1137/188/how-do-i- change-my-monitor-profile-to-check-whether-its-corrupted
Also check what else might have changed on your system between it working and not working? Graphics driver update perhaps?
After renaming the preview cache to it's origional name, previews were not
visible and would not appear in Develop. So I used your link for the
monitor profile settings and it cured the problem! Everything is as good as
new! If you lived near us I would buy you dinner. Many thanks for your time
and knowledge. Denny
On Thu, Feb 21, 2013 at 3:19 AM, Victoria Bampton