Renault Laguna 1.9 DCi 2004?

Having completed a journey of 150 miles without a single problem .I parked the car over-night and it failed to start next day turning over ok but would not fire up. The RAC tried for 2hrs but failed. I have had the car to my local garage who have drawn a blank, having checked the timing,egr valve, no faults listed on the computor, heater plugs all work and injectors are pulsing. any answers please?