no signal gsm with external power supply

Hi, i'm newby on arduino world.

i have an Arduino ONE and an Arduino GSM/GPRS shield, my problem is the following:

when a plug my arduino whit USB of my PC, it work perfectly, but when I connect my arduino with an external 5 volt power supply, seems that shield fails to take GSM signal,

I can't understand , can someone help me? it may be a power problem?

Arduino need at least 7 volt - see specifications - -

thanks, now I'm going to buy e i will try.

Hi, I tried to use an external power supply by setting 7 to 12 volts , but the result is always the same,

my Arduino fails to enter in the "if" to set the variable: notConnected = false; BUT if call it from another telephone it ring, as if he had taken the signal.

but when a plug my arduino whit USB of my PC, it work perfectl. I can't understand , can someone help me? this is part of my sketc (setup):

void setup(){ Serial.begin(9600); while (!Serial) { ; } // set the pin connected to the relay that control the heater as output pinMode(heaterControlPin, OUTPUT); // initialize serial communications and wait for port to open: Serial.begin(9600);

// connection state boolean notConnected = true; // Start GSM connection digitalWrite(heaterControlPin, HIGH); while(notConnected){ Serial.println("GSM not initialized"); if(gsmAccess.begin()==GSM_READY){ notConnected = false; }else{ Serial.println("Not connected"); delay(1000); } } doSmallCall("+393476835437", 1000); Serial.println("GSM initialized");