SimCom SIM900 GSM Module DB: NO RESP

I am a beginner in Arduino Field.
I am using a SIMCOM SIM900 GSM module. When I test it, it usually says,
GSM Shield testing.
DB:NO RESP
DB:NO RESP
DB:NO RESP
Trying to force the baud-rate to 9600

1200
2400
4800
9600
19200
38400
57600
115200
ERROR: SIM900 doesn't answer. Check power and serial pins in GSM.cpp

status=IDLE

Is there separate sketch for GSM Module?
I have read a lot of other solutions but most of them are for Shield.
Please help me...
Thank you!