Can't complete Storyline launch

Hi,  Support suggested I post this here in case someone has had the same problem.

I have a strange problem. I've repaired, reinstalled, completely uninstalled and installed anew, used the clean tool, everything. When I launch Storyline it gets to the opening window and just freezes. I have to use the task manager to close it. It uses memory (about 60MB) but no CPU. I can also continue to launch additional sessions while the frozen screen is still open. I'm on a standalone computer so no network issues.  I've installed as Admin, run as Admin (as not), nothing.

I do see a flash of something in the background right after the window opens and the mouse goes into "waiting" spin for about 1.5 seconds, like it's trying to open itself and then fails. I've tried compatibility for Windows 8.1, 8, and 7 with no luck. I have double-checked my .Net to ensure 3.5 is installed and running.  I also have 4.5 running so maybe that's an issue??? Dunno.

PRODUCT: Articulate Storyline 1