Sounds like dead battery. Mine wouldn't jump start either. AA guy came out, battery was putting out less than 12v, he said it needs to be around 12.5+v IIRC. Plugged in his booster pack, it started, let it charge and was fine until the next day when I got it replaced.
Has a similar issue of not starting or jump starting on my old 1.4. Voltage was below 12v again, turned out it was the battery's earth lead, had become a bit loose so was dropping volts IIRC. Can test this by trying to jump starting positive on battery and negative on chassis I think. Earth lead changed and was all dandy.