Had a 56 reg Scenic II 2.0 DCI in which wouldn't crank, coolant fans came on as soon as starter button pressed, no communication to ECU, no power to ECU. The fuse box at the side of the battery seemed dry, we've had problems before with Renault wiring and heard lots of other stories from others but this one was a corroded small orange wire in the loom just in front of the battery, just inside the protective insulation wrap, just saw a very small powder residue in the loom and there it was, strange, must have just rubbed very slightly. Cut out and repaired.
I couldn't see another similar post so hope it helps someone.
John