strange issue with sim900 gprs shield

Sir my sim900 gprs shield is not working correctly.. initially it work perfectly when i open from box (new) at commands response OK,registered to network etc... after some hours i dont know what happen and i am facing following problem.

  1. Power on arduino mega through 12v 2a adapter, arduino turns on & gprs sheild powkey light and netlight on to red.

  2. By pressing pwrkey 2 second netlight goes off and status light turns on red with low intensity and off a pwrkey released.

  3. There is no light which is on grps sheild except pwrkey light after releasing pwrkey button.

  4. arduino connected to laptop through usb cable and serial monitor window opened. it turns off my laptop when i press pwrkey button for some seconds of gprs shield.

i am confused, disappointed because i find no solution from internet. i dont even know my gprs shield firmware is corupted or is there any kind of short circuit. please help me i have to submit my final year project on 7 december 2016. Sorry! my English is very poor.

Can you give a link the the exact type of sim900 shield you have.

The standard software for the GSM is for the smaller Arduino Uno board, for use with the Mega it needs to be modified.
Have gone back to the unmodified code by mistake.

Is your Mega board a genuine Arduino or a Clone ?

The regulators on some clone boards are a different type and their maximum input voltage is lower.

Sometimes a unregulated 12v adapter can easily exceed that limit and damage the regulator.

Have you measured the +5V power rail when only the 12V adapter is connected ?

Does it work ok for cammond response OK if you run from just your USB cable ?

Have you tested out just the Mega board with the Blink program to make sure thats still working ok ?