that could be so many things, assuming there is nothing wrong with the tool you used to try to communicate with this vehicle, there could have been so many things that affects communication, such as voltage and grounds to the control module, missing or poor connections, data bus communication open or shorted, wrong module installed etc. does this vehicle starts and runs?I will say the first thing I will try will be another scanner, to rule out that possibility. Check all fuses. besides the ecm is there any other module/ecu you can not communicate with ? if so, then that maybe a lead to follow. get a wiring diagram of that vehicle and look at all the modules on that network and compare them to your auto scan results, the ones missing could be on the same network, ( computer data line) disconnect one at time until communication can be restored with the ecm. keep in mind that the hardest thing to do on todays vehicle is resolving a data bus issue, even the most seasoned techs on the field will sometimes have a real hard time resolving it. you will need lots of patience, unlimited amount. good wiring diagrams and of-course an understanding of how they work. youtube is your buddy. good luck.