Dell likes to configure the SSD as a RAID in the BIOS. Even though their Windows installation is not using it as a RAID device.  When it is set to  RAID in the BIOS, Linux cannot see it. For Linux to run, it must be set to AHCI mode. In my relatively new Dell workstation, this is under System Configuration -> SATA Operations.

It "should" be safe (all I can say is that it was for me) to go in and verify that your SATA mode is set RAID (in which case this is likely the cause of your problem), set it to AHCI, and then boot your Linux USB stick. It should then see the SSD.

Unfortunately, Windows will now not boot unless you change it back to RAID. If you were planning to keep the installed Windows system (which I wanted to do), then there is a procedure you can Google for (it might have even been referred to on this list) that will allow the Dell-installed Windows to boot in non-RAID mode. I followed the directions and can now dual boot Windows and Linux out of the GRUB menu.