astra g 1.7 cdti wont start will start

hi folks me astra g 2005 cdti 80bhp is cracking me up,right here we go starts on the button no probs
then i will stop at the shops come out wont start turns over wont start? leave it a bit go back to it
starts then wont happen for days,sometimes i have to leave it a hour sometimes a few mins weird
i no anyway here are the fault codes

p0105 (a) boost pres sensor
p1335 (c) camshaft pos sensor
p0650 (c) mal function lamp vol

the crankshaft sensor has been changed for a vauxhall one still the same?
just wondering should i try the cam sensor

cheers guys