The HP Website has the following support article:
This document describes what to do if the notebook
display shows *black screen* for a prolonged period of time after the
welcome *screen* displays.
In short, it says to update the Recovery Manager program. Did it.
I then came across a posting that stated that the same problem had been
fixed by removing a special character from the computer name. The Costco
Concierge techs who re-installed the OS on my machine last week gave it
the name "Owner-PC" and I hadn't bothered to rename it yet. I thought it
was a long shot that renaming my machine would fix the 90+ second black
screen between the Welcome page and Desktop, but it worked. I gave my
machine a name with no spaces or special characters and the "fix" seems
to be permanent.