The usual problem with any engine failing to start is a lack of fuel or ignition.

Did you do all of the work after it failed to start or did you do some of it before? If you did it before, then what did you do last before it failed to start?

Is there plenty of fuel in the tank and is it good fuel (no water in it)?

I ran my car out of fuel once and had a devil of a time getting it going again as I did not realize it was out. I changed glow plugs etc and it still would not fire. I finally poured a 5 gallon can of fuel into the tank and it fired up with only a little bit of cranking.