Just had this happen to me...
I'd been going through /var/lib/dpkg/status to remove extraneous packages (I've got the total install size down to 4.1 GB), and rebooted to be sure everything worked...
... the computer got to the point where it shut down in preparation for restarting, the screen came back on, and... nothing. Blank screen.
"Huh.", says I, "That's odd."
So I held down the power button to force it to power off, restarted and hit F10... the little text blurb indicating that it was going into the BIOS setup came up, and... nothing.
"Huh.", says I again, "That's really odd."
It did the same for F2 (Startup Test) and F9 (Change Boot Order).
I unplugged everything from USB, thinking one of the drives had gone bad and was hanging the drive enumeration... no change.
I took the bottom of the laptop off, removed the hard drive (just in case the internal drive had gone bad and that was what was hanging drive enumeration), removed the new 64 GB of RAM and installed the old 12 GB of RAM (just in case one or both of the new memory modules were bad)... no change.
"Well, only one thing left to try before I go buy a new computer", says I, as I unscrewed the battery to remove it.
I plugged in the power, powered the machine on, and it popped up a message that the BIOS had been corrupted.
"Well, that's not good.", says I as I sit there thinking... then it automatically rebooted, and automatically went into BIOS setup, where it had reset everything to defaults.
"Well, that's good.", says I as I proceed to set everything back to what it was.
Then I powered down, installed the hard drive, put the 64 GB of RAM back in, and closed up the case... you'll note I didn't put the battery back in... I'm going to try running without it for awhile, since I never use it, and I've got a UPS.
I powered back on... of course the BIOS popped up the same message because there had been no power to sustain the BIOS settings, so after it entered the BIOS setup, I put all the settings back to what they're supposed to be, saved the settings, rebooted and here I am.
I suspect the new F.10 Rev.A BIOS update from HP isn't quite as stable as it should be. I'll put in a bug report.
The moral of the story: Just because your computer isn't booting because of a corrupted UEFI / BIOS doesn't mean all is lost... remove all power and see if it'll reset to defaults.