I have 2 stick of 4 gb and i plugged in just one stick in all slots and still doesent work
Than either its a bad stick or your settings are wrong in the bios. A lot of systems will revert back to 1333 1.5v when new memory is inserted. doesn't mean they all will which could cause blue screens. It will help to know what type and model you have. for all me know its DDR1 lol.