Why won't my 2012 Mercedes Sprinter Van 3500 Diesel turn over or start?

What is your question?

The van has a little over 18,00 Miles on it and i recently drove it from MN to Nd and back. I stopped and fueled up twice and shut the sprinter van down three times during the trip. I got back to our shop in MN that night and the sprinter van ran perfectly fine the entire trip with no sign that anything was wrong. I parked it that night and made sure everything was turned off and went home. The next day I came back to unload the van and when I went to start it the van did not turn over. All the dummy lights clear except for the engine light that stays lit up. I can turn the key in all positions and get all the rings and bells and lights but it will not turn over when I turn the key to "start" the van. I assumed it was battery related and went ahead and checked the battery, connections, fuses and everything was fine...I know there seems to be a lot of issues with the DEF additive and the sensors revolving around the emissions non- sense, but all of the fluids are good and there are no lights coming up in regards to that issue. I'm completely lost as to why this thing wont start, when I used it the day before and it ran fine. To top it all off the closest Mercedes sprinter repair shop is over 100 miles away and when I called there service dept. all they could tell me was it was the battery, which I know for a fact is not the reason...Can anybody shed a some light on the subject and help me out? Mercedes has not impressed at all, I'm very frustrated with there service team and as far as there vehicles go, I will NEVER own another one! very poor quality as far as power-train and motor goes and I've heard and seen nothing but bad things from other people while trying to find a solution to my issue.