newbie and need some fiat advice

[emilou1988]

i brought a fiat punto nearly 3 years ago now its a 1.2 8v active sport 2006 and ever since 2 weeks after getting it home from car giant it dont start you could have it running for over an hour turn it off leave it ten mins and it wont start again, i have to rev it to get it started which produces lots of white smelly smoke from the exhaust i have had 2 mechanics look at this problem and it has been on a computer which said it was a sensor im not sure which one but this has been changed twice now and has cost me nearly £500 and i still have the problem i cant really afford to take it to fiat direct. some people have said it could be the fuel pump or pipe does anyone esle know a little bit about this problem or having the same one as i dont know what to do now Please help me?