Testy car starts one day, wont the next!

[belle007]

I have a vx series 2 thats just had a petrol pump replaced (we thought this would fix the starting problem)
Anyhow, it will fire up fine when it wants to and runs great, but then all of a sudden some days without warning it just cranks over and cuts out, and then it wont crank over at all (no sound). Give it a min and try again with the same result, after 5 or more attempts it has started again, then I waited half an hour and it started 1st time no problem.
Im definately not confident when I go to start it now because I dont know what its going to do.
Help would be so appreciated
Thanks
Belle

P.S
Oh and my key battery is starting to go flat too, sometimes when I press it it wont unlock so I dont know if that is contributing to the problem as i read it might in another post

[strgas]

check your fuel pump relay and fuse swap them with known good ones . check wiring harness for signs of poor connection or dirty connections . check and clean earth return connections . hook up a fuel pressure gauge and check fuel pressure .