Vauxhall Astra not starting or startin sparrodically

HELP HELP HELP Have had this problem for the past few weeks now getting on top of me too now... 3 weeks ago car wouldn't start central locking wouldn't work. Had to unlock car with key put key in ignition absolutly nothing no ignition lights no nothing ( well i say nothing the stereo worked as well did the lights ) had the starter replaced worked fine for 3 days then stopped again.. This time had an auto electrician out tohave a look tested alsorts and said that i needed a new battery.. Got and fitted new battery car worked fine again for a week then once again nothing at all... Have now had the ignition switch changed and again it worked for about 3 days.. And woe and behold you guessed it it stopped working again.. Can even tell now when it not going to work as i can't gain access to the car via the key fob if it unlocks it works if it don't it won't... Can anybody please shed some light on this pulling hair out not knowing whether it will work or not