it loos like firewall issue.how is your PSTN connection

Hi Jaerhee, why you use ip nat inside command on your outside interface? I mean fa 0/0? and best practice you can put modem  in bridge mode and configure ISP configs on your 1841 router (DHCP, PPPoE or any connection type)

Hi Ariffin,Look at the module. if there is red color near the module. It means module is hot plug

Hi Rammany,hope everything will be ok

Try to test on real equipment. Packet tracer is for basic commands. GNS is good but no switch support(