Check connectivity
Check com port. And baudrate
Check setPGPC and choose available connection wisely
Check PG/PC communication
Check the pgpc interface.. then go to connections…check the connection showing in network view and connection tab is matching with s7online or not
Ping the plc ip address from ur pC.
Set PG PC choose protocol you used
Communication Break with PLC n Pc
Check PG/PC interface…If you are using PLCsim, then open PLCsim and select connection as per hardware configuration..
Your COM port is not working, check your Device manager and connect
PLC ONE 