Pleased to report that I now have a working copy of TMG v 9.03 installed on my Windows 8.1 x64 laptop, with both of my projects restored and converted. Thank you for your input, Jim and Virginia; we are fortunate you are a part of this forum!
I had googled the issue prior to posting and saw some scattered references to my errors, mostly having to do with the Windows installer. I was prepared for a deep dive, but it wasn't necessary.
What worked for me:
1) followed the doc created by Jim re: a clean install (topic 14634). Deleted one empty TMG folder, and deleted references in VirtualStore. 2) re-ran CCLEANER utility, including the registry cleanup
3) closed down all processes in system tray (anti-virus, sync, etc.)
4) disabled UAC temporarily
5) redownloaded the TMG trial version to a USB stick, and ran the install from there, running as Administrator.
What was different this time is that TMG asked me where to install the program. If you are not being asked to confirm the install location, chances are there are still remnants of the old TMG install somewhere.
Hope this helps someone else.
Dawn