I'd suggest you disconnect the data cable and power lead from the engine and connect the GSU directly into the ECU without using the I/O board if you were using one.  Use a different data cable if possible. See if the ECU works correctly this way.  You'll get an error where the Temp data is displayed but that's ok.    If it works, I'd reconnect the engine using a different data cable.  Data cables can often be the problem.   If it doesn't work without the engine, your ECU probably has a problem.