In every case, TS reaches the initial splash screen, then freezes until it dumps to the desktop, vomiting (not to use the less polite terms) out another DMP. I've now been through 4 verification procedures, each reporting all files valid. Yes, I start TS in Administrator mode.
My guess is that the next steps are: 1) copy the Assets and Content folders to another drive, 2) have Steam delete all local content, 3) have Steam reinstall TS, 4) copy the old Assets and Content folders into the new installation, instructing Windows file manager to skip files already present.
I'll put this off for a couple more days -- I have snow to shovel, among other chores -- in anticipation of sound advice from other forum members.
