In SharePoint 2010, Normal search is working and People search result is not working fine. Why?

Issue:

Finally, you may have configured the user profiles synchronization & Search services. Also, you may be able to see the number of profiles under "User profile service" and contents under "Search Service". 

Then, If you have used the search box and search results web parts to display the web application contents (not people), you can able to see the documents, forms, pages, etc... But, you cannot see the "people", if you click on the "people" tab in search results page. (or) you cannot see the results, if you have used the "peopleresults" web part.

What will be reason? :)

Reason:

You may have forgot to add the URL to crawl the people in Search service "ContentSource". So, just add the exact url which will start "SPS3://".

Example:

SPS3://km.sensoft2000.com (just an example)

Thats it....