I do not know what you mean by "bailing out of TechTool 10", or what you think caused the original administrative account to no longer work. The tests in TechTool Pro are read-only; only the tools make changes to the disk.
Check to make sure you are using the correct password for the administrative account. I had not logged in to one of my accounts for such a long time that when I tried to do so, I mistakenly used the corresponding password for its Apple ID.
You should be able to boot from the Recovery HD volume, reinstall the system software, and then migrate your user accounts, applications, and user files from a Time Machine backup, or a bootable clone of your usual startup volume.
The relevant Apple Support document:
About macOS Recovery.