A Bad Day Averted
I got home tonight, set up the work laptop and... it failed to boot. Quite often when this kind of thing happens, it's the hard drive (in which case, I would have been off to the local NG shop to get the machine dealt with tomorrow).
Fortunately, you can always look up the diagnostic steps for these things. I found an HP forum with a hard power reset step, and that solved my problem. Which is far better than having to call Texas to make an appointment to visit the IT guys in Linthicum :)