So this is odd: I have a known-good Samsung 830 256GB SSD which my new Dell 8700 Special Edition sees in BIOS, however it's not visible at all in Windows 8.1. This drive works fine in my old computer.
In Windows, I've checked the Device Manager and the Disk Manager, and neither shows an entry for this drive. The Samsung Drive Magician doesn't see it either. I'm using all the BIOS defaults, so the SATA mode is 'AHCI' (rather than RAID; that's the only other option).
Any suggestions on what else to try?