i am sort of thinking that if as MacRS200 said that if there is a faulty censor, it may send some soft of fault codes to your ECU and that may preventing it to start it. why don't you re set your ECU by taking the battery out for about 20 mins and putting back in to see what is going on. not saying it will solve your problem but at least it will clear out all the fault codes and then we defiantly will know something is mechanical.
let us know how you get on.
ok i will try that and see if that helps. i all so noticed to day that engine was turning over slow even when jumpleads were on battery. would that be part of the same problem????