my newhome sewing machine doesn`t catch the bobbin thread?

hi, my newhome machine is around 18 years old and has regularly needed the timing set , it doesn`t catch the bobbin thread again and i have checked that it is threaded correctly ect. but still nothing so i assume this is the problem again, i have read other questions on this site and you say it is a process that requires patience , i am a very patient person and would love to learn how to fix my machine myself, could you please help as it is has sat in my wardrobe for about 4 years as having kids took over the household income