You need to partition and format new drives before they show.
Be sure to look in Device Manager and the partition tool too.
I just built a new computer (ASUS Z170-A, Samsung M.2, XFX graphics, 16 GB mem) & it works fine except for one problem: Windows 10 won't see hard drives, either new or from another computer. BIOS sees them but Explorer won't. It seems like I've forgotten to install a driver but previous builds didn't require one. The M.2 drive (on the MB) works fine but I don't want to store documents on it.
What's going on, everybody???

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