GR64 network registration

Hi, I need some help!

I was working very good with GR64, but suddenly, I get no network registration with all of GR64 I have. I was working with cellular carrier and they told me that there’s no problem with Sim Cards. I was trying with Sim Card with other carrier and result is the same. I have been trying with AT&F but it doesn´t work. Led indicator is on but it does’n blink.

Thanks in advance.