The reset button it like switching your Arduino off and on again, if this makes your code work it may be that your setup code finishes before your GPRS module is ready and so may not get the commands properly, I know seems unlikely, as you get a response for some functions, but it may be worth switching you delay(5000) for something like:
while(!cell.available())
cell.println("AT");
while(cell.available())
cell.read();
This way you only have to wait until you get a response.
PS in your second post you left your IP address in the code