Recording tracks on 500

Hi there! I am new to mpc and I am having problems with creating tracks. I load a programme, assign samples to pads, then lay down the kick, but when I try to lay down the clap it just seems to boost the kick and no clap is heard. Also, when I try to lay down two claps, it just boosts the clap that is heard. I try to lay each sample down on a separate track but it won't do. Any help, please.