Vauxhall Astra car will not start, only occaisionally

they need to check feeds to starter motor and test battery and check all connections to starter and engine earth leads could be ignition switch i doubt 3 starters could be at fault but it could be starter ring gear that is causing the problem

Probably the ignition lock that is sticking causing the switch to stick and burn out the starter motor ,simply requires lubricated to stop this happening.you will probably smell burning when the fault occurs as basically it,s destroying the starter motor.Until some one strips and lubricates the mechanical side of the lock you will just keep on burning out starters unless you physically turn the key back each time you start the car.