first of all, what type of hard drives. also if they are PATA, make sure one is Master and the other is Slave if they are on the same cable. You cant install both on one drive without partitioning it because one would overwrite the other. To set the correct jumper setting there is a little black plastic cap that goes over two pins vertically, move that to the correct location. http://www.mysuperpc.com/pc_assembly/liteon_52x_cdrom_connections_cr.jpg the box in blue is around where you change that.