Sim800L has no signal at all and cannot connect to network

Hi, I have a Sim800L and want to send data to a server. Previously, I managed to connect to the network. After I have discovered the power supply problem (due to my module keep resetting itself) and changed my circuit to supply the Sim800L with 5V and 2A, I failed to connect to any network.
I have checked AT+CBC command and get >80% in voltage. but I am still unable to attach to GPRS. When I perform AT+CGATT=1 , it will always give me an ERROR and when AT+CREG?, I got 0,0 . But I do have signal as when I typed AT+CSQ, I got 13,0 and when AT+COPS=?, I am able to display the network operator.

May I know how to solve this problem please?

What you need is 4V,2A on the module and not 5V, 2A. If you give 5V to it, it will shut down and enter Over-Voltage-Powerdown state.
P.S : You might as well have damaged it if 5V is directly connected to it.