Nissan almera not starting?

My elderly parents 2002 nissan almera 1.5.not starting.sometimes turns but doesnt start as if fuel pump immobilised.also other times nothing on the key at all.occassionally alarm PLEASE WAIT on computer screen.but not everytime.tried replacing remote battery.buttons.case.clean car battery terminals and had fuses out cleaned and back in again.can anyone please help me as my parents are in their eighties and cannnot trust that the car will start when they want to use it. Thankyou