Thanks everyone… I REALLY appreciate the support.
Short story: I installed Kubuntu 13.10 and now it all works (except for Chrome which keeps Aw, Snapping - minor detail).
Along the way I: booted using Knoppix LiveCd to examine things; re-installed the Nvidia drivers multiple times from multiple versions; ran the awesome Boot-Repair-Disk to clean up any grub problems; reconfigured partititions using gparted… It got to the point where I’d get a gui screen to login, but then it would black screen and back to the gui login prompt. I could always get to the console via Ctrl-Alt-F1 and start/restart kdm. I did much of what was suggested and could have responded with specifics, but fortunately don’t need to go there now.
Root cause? I think it was some incompatibility between the Nvidia drivers and the card I have. I’m still using the same video card (two monitors) and it works just fine now. Don’t know what cause the initial problem as it was working before I left for the conference and powered down the system.
I used to believe in the LTS versions, but 13.10 was so much better than 12.04 (e.g., configuring the two-monitor setup was a breeze compared to the 12.04 hoops I had to jump through) that I’ve changed my thinking. The reinstall was really easy given that I have /home mounted on a separate HDrive, so now I’ll just take the latest release when it’s time to move on.
One minor question: why is audio support on Linux (or Ubuntu or for me, anyway) such a nightmare? It keeps breaking and trying to add a USB headset was just an exercise in futility :=)