daf lf 45 wont start?

I have just bought a 51 plate daf lf 45 150 and it drove perfect , parked it up and it wouldnt start so replaced the fuel filter on the tank as it looked bad , bled it up and it started fine , another week later came to start it and it wont start ? both filters are full of fuel , but the primer pump dosnt seem to build up any resistance when you try priming it , swapped the primer pump and no diferen? any ideas ??