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If it turns over and won't start, chances are good that is has to do with a problem in the fuel shut-off relay. Most truck shops would know how to check that. Plenty of fuel no doubt? I usually don't work on engine questions, but didn't want to leave you hanging there. Please get back to me if you need more as all follow ups are included in our fee. Please include the engine make and model. Any other things you feel that are important please mention.
Sorry, I missed that. I would start by having them check the batteries and cables. Are you sure someone didn't accidently hit the battery disconnect switch? This happens quite frequently. IF you are sure that the batteries are "in the loop" then testing them would be next to be sure that one isn't open or shorted out. Sometimes they can fail suddenly. Happens here all the time and almost every day here on this site.
There probably is, but I don't have a lot of background in diesel pusher issues on engines. I will go ahead and opt out of this and allow anther tech here to offer something. I don't know when that might be as we are scattered all over the country.