I started working on a U-blox LEON-G100 gprs modem connected to the PC terminal through UART. Whatever character I enter into the terminal gets echoed back except "AT". When I enter "AT", the modem hangs up. Then I have to reset the modem to make it respond. So, I cant even execute a single AT command. As it echoes back every character I enter until "AT" sequence, I think there is no the electric connections and the UART port settings must be correct too. What would be wrong here? I had experience with other GPRS modems, but this is the first time I am encountering this bizarre trouble.