This is too broad question and without details no one will be able to help you. Also, remember that sudden drops in sales etc. are normal thing. You might be getting many sales during one week, but then you will find out that another week is poor. Check your traffic, test everything. If entire setup is right and didn't change from the beginning, but GA was recording activities fine and now it isn't, then there is some problem with your goals etc. Maybe when you updated your conversion links you did some mistake or something, check everything one again.