thanks for your response. It is random, after turning 7TT off, I got it back, when I turned it on, its gone again. 

Now its working correctly with 7TT switched on. This is a recent development, never had issues before.

Update: The "thumbnails preview" is again gone. Not sure what is happening. Came back after 7TT was turned off.

7TT allows me to use the "Show thumbnails preview" feature. Am not sure if another application is stopping this feature from working. How do I identify the problem ?