Touch Pad Single Click Not Working

Hi,

I have an Inspiron 15 Intel (N5010). The problem I am facing is that: earlier on tap on touch pad, I could select folder, or by double clicking, I could open a file. 

This does not happen now. The tap(which replicated the click functionality of mouse), does not seem to work now. I ran the diagnostic provided on the dell portal and it does not lists any error in the system.

Please help me to troubleshoot the problem.

Thanks in Advance