not working GPRS SHIELD SIM900

Hello, everyone! Need help with GPRS SIM900. Not working shield gprs, when i send AT command it. I tried calling with phone on GPRS SHIELD, it work. But most nothing working. I'm read many forums, and i'm understand what problems can be connected with rx and tx entry. Tried permute jampers on SWserial(7,8 pins on my shield) and arduino serial(0,1). Also change rx on tx(crosswise), no working. No answer to gprs shield when i send AT command. Tried different programs(terminal, sscom32e and arduino monitor port). What may be about my problem?![](