Only 1 SSD allowed in z420

I currently have a Samsung V-NAND EVO 850, 500 gb as my boot drive and a WDC wd3000HLHX-60JJPV1 (279 gb, 7200 rpm SATA). I cannot get the workstation to recognize a second SSD. so far I've tried 3, 2 Samsung  V-NAND EVO 850, 500 gb, and a SanDisk 480 gb SSD. none are recognized in the bios, or in Device Manager or Disk Management.

I want to replace the Sata with another 500 gb SSD.