will sometimes not start, it turns over but won't fire up! when I return to it 2hrs later it starts up!

It is a 2.0 diesel, I have put on a brand new crankshaft sensor, changed the ECU unit (water in old one), changed the relay switch under the glove compartment, checked the injectors for diesel getting through.When I try to start it up in gear & the car****** the next turn sometimes starts it up.I WILL GLADLY SEND A GOOD DONATION IT YOU RESOLVE THIS FOR ME THANK YOU.