Car won't start, light with key flashes - but the car is getting power?

Hi All, i know this question has been covered i just wondered how people have got on...my car cut out last week and i could start it again with giving it a lot of gas and it was high revs for a few minutes, happened again the other night and came on again. The next day - nothing. A light on the dash flashes and it looks like a key, a few people have suggested a changing the transponder aerial (approx £20), phoned a garage and they said it sounds like my ECU and quoted me £400....its a big difference for what sounds to be the same problem. with Christmas coming its definetley £400 better in my pocket.

HELP!!!