help The needles on my knitting machine keep falling out?

hi I have been given a brother KH 830 knitting machine (second hand) I am having problems with it. The carrage is very hard to push and when I do the needles fall out . I have changed the sponge needle bar as the felt was flat but since I have put it back the needles come out when they are in position E can anyone tell me what I am doing wrong. I am unable to cast on or do any knitting please help