How use gsm SIM900a module A6

Hi guys, I have a problem with a gsm module, this, so to speak!

I can use it perfectly, the only problem is that sometimes it does not respond anymore, that is in the serial nothing is printed, until something occurs (I do not know what) and the module returns to work.

So I thought to reset it when the condition of having no response, but the case that wanted to buy the only module on the market that does not have a reset pin.

Has anyone already had this inconvenience?

Thank you all!!