GSM module SIM 900

Hello Every one i have bought new gsm from ebay but when i have insert sim card to GSM it is not connecting to network . I have tried other operators sim card also it is same situation. Who can help me . Thanks for advance.

You could always start by posting a link to the product in question?

make sure the unit has enought power (4.4V and 2amps) otherwise it will not switch on, make sure you are conected correctly RX and TX lines in the correct place. what lib are you using ? your AT command configuration could be wrong