What I've tried/know so far:
1. I can reboot into recovery and TWRP v18.104.22.168 pops up just fine. However, it also asks for my password, which I can bypass by hitting cancel.
2. I have tried to factory reset, but after about 5 seconds, it says failed, during "Updating partition details"
3. I have tried to advanced wipe, but it will only let me wipe cache, and not data nor Dalvik cache.
4. I can't restore anything because nothing shows up under restore.
5. If I go to restore, the size of the various parts (data, system) seems right, but I can't back anything up. It always fails during "Updating partition details"
If anyone can be of any help, it would be greatly appreciated! I'm not super techy, but I'm willing to try whatever at this point. I'm pretty much resigned to losing all my data, which isn't a huge deal; I believe most of my stuff is backed up.
If someone can say definitively that I'm SOL, then let me know. At least I know I can move on. Some have suggested that this could be a hardware failure related to my flash memory, in which case, I don't think there's anything I can do (unless there is).