ford transit 2001 deisel will not start?

ford transit 2001, 20lt deisel will not start, and it allways started first touch, i have renewed the battery in the fob and reset it so it opens and locks the doors ok, theres plenty of fuel up to the injectors, i drove home one night in it, it ran perfect except for the speedo went off then back on again, got home switched the van off, then it would not start an hour later, therse plenty of life in the battery, i only have the blue key but has aways been ok , do these keys loose there memory and what needs to be done, does anybody think the speedo going off has anything to do with it not starting, if you have come across this fault, please please help