Assuming the following has already been covered:
Power on, CG150 installed correctly, USB port configured correctly, wiring correct pins used and not swopped, terminating resister(s) OK, baud rate on the service tool set correctly, service tool is set to online, all nodes are broadcasting at the same baud rate, lines are not too long for the baud rate used, all nodes have a differing number.
If still not communicating, then disconnect all nodes except for one and check comms again. Do this for each node individually. If all OK individually, reintroduce each node one at a time until comms is lost.