Sim 800l blinking 7 times

My gsm module used to work properly, but suddenly whenever I'm giving it power, it keeps blinking 7 consecutive times then 1 sec delay and then again blinks 7 times. I have tried connecting it through 3.7V of 1800mAh lipo battery. I have also tried by pulling out the sim and again inserting it few moments later. But nothing is working.

related to his other post