Few SIM800C AT commands are not working

Hello Ravi sir.
I am using SIM800c module. Its taking basic AT commands but while I am sending GPRS related commands Its getting error. And also while sending a call command (ATD+mobile number) its showing me no “dial tone”. I am giving power to the module through Arduino uno board and connecting the powerkey to the ground through resistor. so is it a problem of powerkey or supply? and if u have any working circuit or schematic related to powerkey please give me the reference of it .

Thanks for support in adv,
Nivrutti Mahajan

Module needs 4V 2A supply. If you are suppling through USB its not going to source more than 500mA. So give a proper power supply first and try.