The part entered Hibernate/shutdown mode without a proper wake source and I am not able to communicate through serial wire thereafter

The problem here is that the serial wire cannot communicate with the part when it is in Hibernate/Shutdown modes. So overcome this situation, enter the serial downloader mode by pressing the BMODE switch (SW1 on the Ez-Kit) during reset. Now the part waits for the data over UART instead of executing the user code and thereby not entering the power-down modes.