A day later and no specific help arrived. My only suggestion is an ancient HP Deskjet trick: "pull out all of the ink cartridges, then power down the unit. Open the paper tray, hold down the buttons and turn the power back on. Release the other buttons." This once (uh, 2000? 2002?) triggered a Mass Reset on the Deskjets.
Is this really a $200 printer, by the way? (I see an Amazon reseller is putting these out for $199... really?)
Oh - if the Power Button isn't activated when the other buttons are held down, release them and then hold the power button down and see if the unit starts again. Normally, I just tap the power button these, but I seem to remember a "held down" button triggered this Reset function.
I'm not sure this will solve the Paper Feed Sensor problem, however.