What year is the A6? Which motor? Did this happen after the car has sat for a period? How long? Can you insure that fuel is making it up to the injectors? (cloged fuel filter or fuel pump not running) How about spark?
I have just had this problem when I moved the car off the drive and when later tried to start it - no luck. Had to call out Audi who told me the engine floods if you have the car going for less than 2 minutes in cold weather and then try to start it again! I was told this is not a fault but an Audi "quirk". You need Audi to come and get it started again otherwise your warranty maybe invalidated as you need to switch off the fuel pump to clear the problem!! argh