my rover 45 has problems starting?

i bought the car several months ago,and all was well untill about a month into owning it,i started having problems with starting the car.
this problem would normally occur after having used the the car several times in the day,and then could play up whenever.
ive had the cranksencer changed,as my garage said that,s what the scan came up with,and they have checked all major componets,but the problem has persisted.
could it possibly be something as obvious as just needing a full service as has been pointed out to me.
the car is a 2.0 litre steptronic v6 auto,x reg.