Turns out to have been faulty hardware. (It finally "gave it up" with the POST error: "929 Fatal MCA Error
CBO / LLCO error in CPU0 Core 671 08864 Data L2 Cache Data Read Error CPU0" after being powered on for 45 minutes one day.)
So I got an RMA, boxed the unit up and dropped it off at FedEx with the pre-paid labels HP sent. The next day they processed a refund. Apparently, since I ordered without a GFX card, they do not exchange faulty units in the first 30 days as the web store states. So I had to duplicate the config for a new order.
The bad news was, after waiting 19 days for the new one, spending nearly 5 days trying to get the thing to work properly (or give some concrete info as to whether the problem was software, hardware, faulty product, or cockpit error) then having to re-order the workstation, the price went up $200 for the exact same product.
And I am now waiting again on a replacement for the croaked z800, so it will likely be 5 - 6 weeks from the time it died just to get working replacement hardware (laptops and tablets are no substitute, I can ASSURE you), and another month before I get all the apps back on, configured and running "as usual". So a total of 10 - 11 weeks of much reduced productivity because of a workstation failure - makes one think seriously about having a "hot-spare" just in case.
Anyway, I guess we get to mark this one as "resolved".
wmc