Arduino GSM shield status LED goes off even after providing external supply ?

I'm trying to make voice calls using Arduino UNO and an official GSM shield(M10). As UNO couldn't provide enough power via USB, I tried giving external power supply (as suggested here: http://forum.arduino.cc/index.php?topic=212741.0).

Also, I tried connecting both external supply and USB as stated in another thread (http://forum.arduino.cc/index.php?topic=74076.0) but couldn't fix the problem.

any solutions would be much appreciated ?

Thanks in advance,

The USB supply should be sufficient enough, when it comes to powering your shield. I think the problem is somewhere in the coding which makes the status go off all of a sudden.

Bentenny10: The USB supply should be sufficient enough

Really? Even though the product reference page states:

It is recommended that the board be powered with an external power supply that can provide between 700mA and 1000mA. Powering an Arduino and the GSM shield from a USB connection is not recommended, as USB cannot provide the required current for when the modem is in heavy use.

Although in the absence of any further detail I am tempted to agree with your diagnosis.