After flat battery audi a4 now wont start, hazard lights flashed then no turn over at all

SOURCE: 1999 Audi A4 Locking mechanism

It sounds like the vacuum pump has gone out. The locks are vacuum-pump operated, and they're known to eventually fail on these and VW cars. Check that out - in my 99, the unit is in the trunk, passenger side. You have to remove the storage well between the wheel arch and the taillight, and pull the carpeting back, and the unit is down there just a bit below floor level.

SOURCE: A4 Turns over, but won't start

it could be your altonator!!

SOURCE: 1996 audi a4 ignition kill switch wont recognise car keys

HI,MARK,THE SIGNAL FROM YOUR KEY IS NOT GETTING TO YOUR IMMOBILIZER.THE PROBLEM IS MORE LIKELY AT THE PLUG ON THE READER COIL ON THE IGNITION.YOU WILL HAVE TO BEND THOSE TERMINALS SLIGHTLY CLOSED AND INSULATE THE WIRES SEPERATELY.THIS FEATURE IS PART OF THE VEHICLES SYSTEM UNFORTUNATELY,ANDY

SOURCE: 1999 audi a4 oil reset light

Turn off the ignition press and hold the button on the leftside of the display while turning the ignition on it should say service oil on the display pull out the button on the rightside of the display until the service oil clears

SOURCE: 2003 audi a4 1.8t ECU/emission control system warning light flash

No I am a mechanic at Audi. The problem is that the the air flow to the central tappets may be causing the air flow sensor to trip and that is why. Try putting a small amount of WD40 into the petrol and that will work, its a very common problem.