Hi and welcome to MR greenclaws.
Sorry to read about your problems.
There isn't much left to add to your procedure described in your first post.
What puzzles me is
I can see that the two drives in the e-reader exist to the pc using the windows disk management program.
As the 300 has no external cardslot, but it might be the SETTINGS partition.
I can't do a hard reset because the thing won't turn off, when it seems to run out of juice it still displays the Opening Book screen but
it is turned off (after a reset), but a e-ink display will not clear when the power is shut off.
You might try to alter the hard-reset procedure:
already hold down the two (2) buttons "arrow-down" and "0" while power on, and hold them down until (hopefully) the reset all screen comes up.