Problem with peugeot 206?

First i'd like to say i don't know alot about cars so sorry if this isn't very detailed. The car is a peugeot 206 1.4 deisel 03 plate. The car will start up fine first thing in the morning or if i havent used it for a while but after i've drove the car and turned the engine off it wont start again for a few hours. If i try to start it before that it just comes up with an 'Air bags' sign on the dashboard and wont turn on. It also wont start on a hot day which makes me think its something to do with the temperature although the temperature guage doesnt get high. When it is goin to start another light comes on which sort of looks like a valve but i'm not sure what this is. I've taken it to a garage and they said it could be a problem with the ecu which would cost me over �1000 to replace and someone has also checked it on a computer and said the fuel temperature is too high. I'd be very grateful for any advice or tips. Thanks.