This story could be told in order of discovery. That would be more fun. But I'm going to explain it as plainly as possible to make it more useful. I have a KVM switch (Keyboard Video Mouse) that lets four computers share one keyboard, display, and mouse. Unbeknownst to me, the keyboard started generating a rapid stream of ESC [ D (back arrow) sequences. I'm not sure whether it is all the time or just some of the time. The next time I booted one of the computers, it seemed to fail to find its hard drives. It was more than a decade old, so rather than fixing it, I replaced it. I now think that a continuous stream of backarrow keys confused the BIOS (or the RAID card BIOS) when the machine was booting. But at that time, it seemed to be a simple case of old hardware wearing out. Another computer had different symptoms, but again showed disk problems. When I did disk diagnostics, I was puzzled by the results: no problem. Eventually, I found the keyboard problem and have thrown the keyboard away. I have no idea how long it had been misbehaving. Lessons re-learned: - symptoms don't always point clearly to the disease. - conclusions should remain provisional - it's amazing how long you can overlook a stuck keyboard key - apparently I really only use the KVM for booting; it would be nice if PCs had been designed to be happy headless