Precision 3620 hang

I've been setting up a Precision 3620.  Everything worked well for about 3 days.  The last step was populating user data from an external drive via USB.   When I returned to the machine the copy had finished, but programs wouldn't launch - for example Firefox said that it was already running, but the process didn't even show in task manager.   Some sort of Dell "Command update" window was flashing.

A reboot just resulted in a hung desktop: the hourglass showed on the task bar and nothing could be selected.  Task manager hung with a blank window.

I still had the firewall on, so I couldn't attach with event viewer from another computer.   But I did have a drive mapped.  I saw some Windows Update activity logged, but couldn't see if it was just checking or if there was an actual update.

I'm giving up and resetting to the factory OS.

All this just to compare notes in case it turns out to be a bad Windows or Dell update.   I'll definitely checkpoint the install.

Oh, and the Boot CD wouldn't recognize the Bitlocker recovery key even though the Bitlocker ID matched.   Guess I'll have to go without Bitlocker on that PC.