LED in UNO constantly blinking

hey
I'm new to Ardunio and I'm trying to interface UNO with a GSM. The interfacing works when the LED is on continuously. But sometimes thr LED starts blinking continuously and then there arises problems in the interface. Can you please suggest something :~

Can you please suggest something

Post the code you uploaded to the Arduino?

What LED?

What is the power source you are using?