Hi it would be worth first checking that the gearbox oil is at the correct level to check this drive the car for about 5 miles then come to rest with the engine still running,wait for 2 minutes then clean/check the oil level,the dip stick is very low down on the passenger side of the gear box, if the level is fine i would put money on it being the starter inhibiter switch on the side of the gear box,if you need any help please get in touch.
Russ
www.rtmechanics.co.uk