Starting

my car was running fine then i went out one day and the doors wouldnt unlock with the keyfob after a couple of attempts it worked! then i got in the car and turned the ignition on which was fine then when i turned the key a seconed time to start it the starter motor turned but the car wouldnt fire/start. i thought it was the key fob so changed the battery now the car locks/unlocks fine but still the car wont turn over or start, also the speedo needle vibrates when trying to start it. the starter motor still turns though, any ideas? i had problems with the sensor by the gearbox before (intermittent starting)but its not that as ive checked it.