Did you do the conversion, and if so (or if not), how do you feel about doing it again? I've got a couple of Nook HD+ devices I've rooted and changed the OS to Android via Cyanogenmod (which is now Lineage, I think) -- and I had a heck of time with Android 7.1 (Nougat, from cm_ovation-ota-NMF26Q.161222.zip image), it wasn't stable and would drain my battery in a few days. I had to leave it plugged in all the time to basically keep it bootable, and if/when it goes dead it's a pain to get it to come back up.
I tried various flavors of Android 7 on a couple of HD+ devices and never was happy with it -- the most stable Android OS I've found (and I've done a *lot* of experimenting) is 4.4.4, Cyanogenmod 11 ("ovation"), there's a good guide/walk-through on installing it at
https://www.xaprb.com/blog/2015/01/1...d-nook-hdplus/
If you wanna stick with 7.1 then I'd recommend booting to recovery and do a wipe data/factory reset for starters, if you've no clue on how to do that there's a nice guide at
https://nookhdplusandroid7.wordpress...k-hd-for-free/ [Edit: The guide will show you how to created a bootable microSD card so you can load recovery on your non-booting HD+)
Hope this helps, if you've got more questions just let me know!
(I'll be happy to write up a step-by-step guide with links to all specific needed files if you'd like, it's literally three zip files and one freeware disk imager prog to do all this so don't sweat)