I can't speak for Windows 10, but since you don't see this 2nd instance drive (E) with Win 7 or your other XP system, I give the blame to Win 10. And, I think you are correct on a clean install (although if the Win 10 you have is an upgrade, it likely will not let you do a clean install, courtesy of MS). Too late for Win7, but if you had a Win 7 environment still, I was going to ask if you had a system restore point just prior to the glitches, and/or a registry backup prior to these events (again, Win 7 scenario).