A8 4.2 Starting problem, Suggestions please

[iggypoppy]

Hi All, Can anyone suggest what I may need to do to repair my 2005 Audi A8, 4.2 petrol? It has 94,000 miles on it. Here is a brief list of the order of events.
1. The alarm started going off randomly some weeks ago but the remote still worked to stop it and the vehicle ran fine.
2. Drove to work one day and all good but would not start in eve.
3. Called out the AA roadside assistance, 2 men couldn’t start it and even changed key battery.
4. As it was still at work the next day, I tried it while waiting for the recovery transporter and it started and ran normally.
5. Took it home and parked it.
6. Next day it wouldn’t start
7. The remote key fob does nothing, electric windows don’t work nor central locking. The dash lights up when opening the doors and shows the mileage, radio works as do the interior lights
8. The key in the ignition has no response
9. I examined the passenger footwell and it had a pool of water which I have now dried out. It will need the drainage tubes cleaning but the car is under cover in the meantime.
10. I did disconnect the battery so it did not flatten until I had time to look at it and it was unconnected for about 4 weeks but kept on a trickle charge system.
Any help would be much appreciated as I am no technical wizard and can only do basic jobs. Feel free to call and have tea and cake whilst looking at it. Lmao. Thanks Guys
Regards
David