Hi Pratik,
Did you write the board with a low power application? If yes try to wake-up the board. Depending on application flashed, it is a pin/ timer... that wake-up the chip from low power.
A second approch could to use a jlink command line application. If the "connect" command is not working, try to use "unlock kinetis" command. Something like:

Let me know about your result,
Regards,
Ovidiu