Here are two more things to try... a hard reset and if that doesn't work, then try what has been called an unbricking reset. Please remember that you may lose whatever is on your Reader at the time.
Hard Reset (Revert to factory settings)
https://wiki.mobileread.com/wiki/Sony...ctory_settings
Edit: Also I see that the wiki has hard reset instructions here. I don't know if this is identical or yet another option for doing a reset. And, of course if you haven't tried it before, you will want to try a soft reset before any of the others.
Unbricking Reset
(This one seems to require a reflashing, so I probably wouldn't try this unless reflashing got you in the mess in the first place, or unless you really know what you are doing.)
https://wiki.mobileread.com/wiki/Sony...8Unbricking.29
I hope one of these works for you.