After checking the video cable and noting that there was in fact a grey signal getting to the monitor (it was not totally black) I eliminated for the moment the possibility that the screen had broken. Then I tried the big blue power button on my Fractal Design case, but it was unresponsive. One limitation of this case is that there is no reset button, so I was forced to power off using the big switch on the back... not something to do lightly.
When the computer booted up I waited for the first screen, which displays BIOS information, and quickly scanned it and those that followed in case there was some error message. These text mode screens had no useful information for me. Then the first graphical screen presented a "Windows loading" image, but this flickered out to black. I waited until I could not sense the hard drive spinning any more... but the screen was still black. Windows had not loaded. Oops. This was looking like a hard drive failure of some sort (though I had heard it spinning, so it was not completely dead) or a virus. (When in doubt, blame a virus.)
In cases like this I have found it best to completely shut down the computer and unplug it from the wall power. That might be the best tip you are going to get today. Unplugging the computer for a minute or so ensures it is off completely. Turning off the power does not. A more radical step is to open up your case and use the manual reset button (or jumper) on your motherboard to clear the BIOS. But personally, I have never had to do that. (Famous last words, I know.)
After restarting the computer it went through the initial BIOS screens and then gave me something I have never seen before. The "Windows Resume Loader" screen presents two options: "Continue with system resume" and "Delete restoration data and proceed to system boot menu". Apparently this is a feature of Windows Vista and Windows 7. Since I am more familiar with Windows XP and had never used hibernation features before this year, I have been lucky enough to never encounter it.
OK, so the hibernation info had somehow become corrupted. No problem, I'll just cursor down once to the second menu option and hit Enter. Except... no cursor keys. No Enter key. Keyboard acts frozen. Yikes!
If this happens to you, here is the problem and its solution. Problem: At this screen the computer responds only to a PS/2 connected keyboard and you likely have a USB keyboard. Solution: Tell the BIOS you have a USB keyboard.
So, reboot and immediately tap whichever key gets you into your BIOS setup. This might be F1 or F3 or Del or something else. Consult your BIOS manual (or check online) to see which it is. Or simply read the first screen where it will tell you -- but be quick!
Once in your BIOS, you want to find a setting that reads something like "USB legacy support". My Gigabytes motherboard uses the Award BIOS, so I chose the top-level menu option "Integrated Peripherals", found the "USB Keyboard Support" item and turned it on. Don't forget to "Save" or "Save and Quit" out of your BIOS. The system will resume. This time when it gets to the "Windows Resume Loader" screen you can use the keyboard to choose the second option: "Delete restoration data". Windows will boot and all will be well.
But here's the totally stupid, inanely dumb and incredible user-unfriendly part.
In order to change the BIOS settings so it would recognize my USB keyboard I had to use my USB keyboard, which the BIOS did, in fact, recognise. In Windows the computer also recognises the USB keyboard with no special jiggery-pokery. It is only in between loading the BIOS and loading Windows that the computer will not recognise a USB keyboard unless you have explicitly told it to. What possible sense does that make?
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