The computer is a Dell Optiplex 780. This has a PCI Express 16 expansion slot (16,8,4,1; the black slot upside down in this image) http://tinyurl.com/sry5ycc
The SSD is a Crucial CT11437367 MX500 250GB 3D NAND M.2 Type 2280 http://tinyurl.com/yd4osybg
I have also got a PCIe to m2 adapter to take the Crucial SSD card and allow it to be plugged into the PCIe slot on the MB. http://tinyurl.com/we4hg6t
Assembled it all OK, and switched on the computer, but no sign of the SSD in Explorer. Removed the lid of the computer and could see LEDs alight both on the adapter (red and blue) and the SSD card (red). They were permanently illuminated, i.e. no blinking.
I switched off the computer etc and re-inserted the card into the expansion slot, but still no joy. Removed the adapter plus SSD card and checked the card in the caddy I had been using it in on another computer, and it was working OK so I've not blown it.
I've a feeling I have to 'mount' or 'install' the SSD card in order to see it, but I can't remember or find out what I have to do. Any suggestions?