dear lall hope you can help me with the following

I have an audi a4 1995 with a starting fault at the moment
The car turns over but will now not fire up
Prevoiusly car was turning over and then fireing up/ starting for 2 seconds and then cutting out. So I thought it may be a key / immobiliser fault
Vagcom Locksmith engineer has checked keys and the reader coils and they are both fine- the car recoginses the keys as correct- but car will still not start after turning over ( execept for one or two exceptions when it will start/ fire up and then cuts out after two seconds)
There is an audible alarm in the engine compartment- similar to when you leave the door open but not its not very loud and stays on for 2 minutes when you try the ignition

Im wondering whether this has anything to do with the same starting fault -?? as I bever heard the alram before in over 10 years of owning the car. Im told the audiblealram may be coming from the ecu in the engine compartment- ??


The VAGCOM engineer did not pick up any fault codes - when he checked the car out
Also no after market alram fitted. if it is not the imobbilser or the reader coil as the vagcom man said no errors came up
the car has had an A4 new reader coil fitted 3 years ago - so audi advised its very rare for reader couils to go twice

have charged the battery and the car actually fired up and stayed ON when i tried it the next morining !. but then turned off and it wouldnt start ( turned over fired and then two seconds later went out~). An hour later it wont fire up- battery seems fine as ive chareged it and its very new


Really desperate to find out the fault so any help appreciated
thanks
Steve