But fortunately after some days, I tried to re-animate my mobile by re-installing the firmware several times. Thankfully, it returned back to normal but everything was erased and reset. But I'm happy, it's back to normal. Literally, it was a waste of time to update the firmware.
So, you get it now, if you have any LG mobile, be careful when updating your firmware. Otherwise, you know what will happen LOL!