Piaggio porter starting problems

Hi
I have a 1998 piaggio porter hijet the engine turns but wont fire up I have changed the plugs and cleaned the injectors but still wont fire up . Today I even placed anew battery and it fired uo right away but after driving it aroud for some time it would not fire up again. It seams that the problem is intermitent. Can some body hint me what els I have to check pls thanks

Alex

Its possibly the 2 little wires on your live battery terminal, one of them is probably on the verge of snapping.

Or maybe the fuel pump is intermittent? Listen out for it when you turn the ignition key on.

When trurning the ignition key a humming sound can be heard , I am assuming that that is the fuel pump