I was a diesel mechanic many years ago and that was one of the first steps they taught me in technical school. Check the obvious stuff first. I can't tell you how many times I've been called to work on a piece of equipment that wouldn't start just to find out it was out of fuel or the operator didn't have his foot on the clutch. I've even done it myself. I replaced a battery on an old truck because it wouldn't start. It turned out that the problem was the corrosion between the cable and the clamp.
