Well firstly the "slave" terminology you are using is meant for PATA not SATA. SATA has its own individual port to the controller unlike PATA which would support two devices on the same ribbon. If they are clashing it likely means that you have an OS on each drive which conflict at boot up. You can get around this by deleting off the partitions on the HDD (assuming you want to use the SSD as the OS drive) or you can put one of the drives on a separate controller. Some motherboards come with two controllers. If your board has 8 SATA ports it is very likely that two ports are on a separate controller.