Hi Pankaj,
- Is your Smart Search index up-to-date (rebuild)?
- Can you confirm that your search query returns results (via the Smart Search application)?
- Have you specified the no results text in the web part properties?
- Are there any related errors in the event log?
- Are you using update panels?
There are additional debugging settings in the web part that you could consider using. Maybe the questions above help you pinpoint the issue.
Cheers,
Jeroen