PT 2018.12 won't launch after reinstatement

[bruceup]

I just reinstated my annual plan for Pro Tools Ultimate, and was running 2018.12 on Mac Pro 5,1 High Sierra with an HD i/o flawlessly (with no plan) until the reinstatement this morning. Account and iLok show licenses are active and good for another year. Now PT no longer launches at all. I uninstalled, reinstalled 2018.12 and hd driver, nothing. All I get when I double click the PT icon is a short flash and then nothing, no plug scanning or any of the usual ritual (just spinning beachball). System shows that PT is active, but it's not, and only a force-quit will stop whatever process is going on. I can't trash prefs, caches and such since it won't launch. I'm stumped and up against deadlines of course. Any ideas?