The key to this is to use needle-nose pliers to grasp the grate between the black plastic circle and the edge of the mini's case, and pull upwards (away from the hard drive beneath it). It will snap into place, and then the screw holes will line up.
Probably the same as any other PC, not specific to this tablet. Maybe the SSD is not seated properly in its connector, maybe there’s a physical problem with it, maybe it doesn’t contain a bootable operating system (the volume’s EFI data is wrong, there’s corruption to the filesystem, &c.).
