1997 Ford F350 Truck won't turn on most of the time

Bought this older low mileage diesel truck last week. (53,000 on a 1997) went to turn it on over the weekend and it won't. Checked battery and they were dead (although marked Feb of this year) so we charged them. (And I got blame for leaving something on which I did not do) charged them up and the truck would still not turn on. Husband got out the volt meter and it is showing charged so he wanted me to just put the key in and put on accessories so he could keep checking. Instead, I saw all the lights go on and said I thought I could turn it over and I tried and was able to turn it on. Hmmm so we tried wiggling stuff to see if we could make it not turn on. All was well. That was yesterday. I went out now to turn it on and nothing! Lights light up as if it will go on but motor will not turn over, no noise at all. So I got out the volt meter and I checked and there is charge. 12.8 or so where do we start? What could be wrong.