Please do not post questions more than once. It makes it difficult for you as well as those who will try to answer. I don't have an answer for you. However:
What operating system?
What version of Lightroom?
How much RAM?
Did you install anything new?
What version of Camera Raw are using in Photoshop CS5?
If you can provide more details, it might make it easier for someone to provide you with an answer.