I initially installed Win 10 on an SSD and then migrated it to an M.2 and removed the SSD. Works fine. But I would like to reformat the SSD and use it for storage. When I reinstall it and set the M.2 as 1st Boot priority in Bios, it keeps defaulting to the SSD and the M.2 is then listed as inactive in Disk Management. If I connect the SSD after normal booting, it will not show up in disk management at all. Any ideas? Thanks very much.
Try connecting the SSD with an external enclosure, format it then and see if it works OK after that. Also check your system manual/support site to see if there are any special tricks to getting it to boot off M.2 when the SATA drive is in the system.
I didn't have an external enclosure to use, so what I did was to boot into Linux from a thumbdrive. The Disk management in Linux listed all drives, perhaps because it wasn't detecting the drive with Win 10 as a boot drive. I was then able to format it there and voilà! Thank again for your help.