The other day, I had one of those scary moments where my Windows computer wouldn’t boot. Panicked, I started to disconnect USB devices, check connectors, and was just about to take the cover off . . . when I noticed that a manual was lying on top of the computer’s keyboard. Its weight was sufficient to press down on several keys that, when the computer scanned the keyboard on bootup, registered an error. I removed the book, restarted, and — much to my embarrassment, but also to my relief — the computer booted.
Failure to boot can also occur if you’ve set your computer to boot first from CD-ROM and have a CD in the drive that looks enough like the system to interest the computer, but not enough to boot. This can also happen if you’ve set the computer to boot first from floppy, and there’s a bogus floppy disk in the drive. Remove either the CD or floppy, then reboot.