my sd card for my nintendo dsi console doesnt work?

hi can anyone help me? i have a nintendo dsi console ive brought a sd card and a sd adapter for it and when i put them in the console a message comes up the card in the sd card slot entered says can not be used does anyone know what the problem is? thanks also i brought a r4 card and when i put that in the back of console and switch it on nothing comes up in the menu does any one know what the problem is there? thank you