I just put a computer together myself and the A Drive cable is totally different than the Hard Drive cable and it isn't even the same size. I installed a Motherboard, all the drives, internal PCI cards, processor, case, power supply, and my Bios detected everything and so did my OS. The A: ribbon is smaller than the IDE ribbon and it has its own slot on the motherboard. There is a plastic pin on top that forces you to align it properly. Mine did.
Your Bios should also detect that you have a A: drive installed. Maybe your Bios is not set to auto detect and the A: drive is turned off. Or maybe you've turned off your Bios Plug and Play, and it is not detecting the A: Drive. The Bios should definitely detect the drive first.
Another reason maybe that you are using another OS and you have turned off the option to search for a new A: Drive every time the computer starts. Doing this was suppose to decrease boot time, but in your case it might be the root of your problem.
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