I left the machine with the tech guys.  It will be some time before I know any more from them.
I will report it here for anyone interested.

I'm 99% certain it is not a hardware issue with either my computer's main hardware or the graphics card.   The problems only came about with respect to the update and my attempted rollback.  Everything else had been operating 100% perfectly.

I could not get any configuration of Windows 7 to launch properly after the rollback to the old restore point, and I strongly discourage anyone from relying on the restore point if any updates have altered your registry with respect to video drivers.

This is now two issues, one with Windows 7, and one with Carrara.

I agree with what was said just above:  I know for a fact Carrara does NOT uninstall cleanly.
And if it is actually leaving additional hidden keys that do not uninstall or reinstall properly, I'm really angry at DAZ, and their needs to be a complete and clean uninstall tool made for it.

It has now been two full business days without a response from DAZ support (other than an automated acknowledgment), which tells me they're either busy with issues, or else they're stumped by my problem.   Either way is not good for me.