A whirring noise? was it turning over at all? When my batteries have died,, I got a clicking noise. or was the whiring from something else? Maybe the belt snapped? (that is a very wild stab in the dark!).
whirring noise sounds like the starter motor is spinning but not engaging with the flywheel. sometimes you can hit the top of it to shock it into engaging, but i doubt its got easy access.
if that's the case then there's nothing wrong with the battery.
What did you use to charge the battery? Sounds like a silly question, but the V6 has a battery with a large amount of cranking power and thus requires a powerful charger! Mine ran out of juice a couple of times and the best way to get it going was to either jump start it from another motor with a big battery (alot of modern diesel engines have a fairly pwerful battery), or to call out the rac/aa and have them use their booster packs.
Look underneath and see if the earth cable has snapped or loose,my Brera stopped and would not start, the lights and dash lit up but nothing happend when I tried to start it,called out the AA they spotted it after a few minutes fixed another one on which they had with them, I started up and off she went,he told me to leave the engine running for half an hour when I got home and have had no problem since.
My money is still on the battery. It went down after the cold night on Tuesday. If the earth wire had snapped, the starter would not spin and I suspect that other warnings would appear. My charger is only small but it has never failed to charge a battery before, certainly enough to get the car to fire. My engine is a V6 so no belts to snap and anyway that would not result in a whirring noise, just a horrible clanking. Going to pull the battery in a bit and get it flash checked and replaced if required. This car did kill a battery at 2 years old before I owned it. The current battery is about therefore 6 years old and probably about due for a swap.
Battery checked by shop in Nottingham. Apart from being dead flat, no signs of damage or deterioration. 24 hour charge off the car and after a bit of cranking, the beast fired. Just had to reset the electric windows, date and time. Everything else seems to have retained settings. Suppose I will just have to drive the car more to keep the battery fully charged.