Steve, my car went flat while I was in Japan and there wasnt enough current left to jump it, or to register a charge using the trickle charger.
I got around it by connecting jumper leads at the back, connecting them to another car to get charge going in, then connected a charger to the terminals in the engine bay, which then registered charge.
Left it for 24 hours and hey presto
That said, it sounds like there might be another reason for your car failing to start