I put my spare parts together into a working PowerBook 1400cs. Minus a keyboard, for now, so it has an external ADB connnected. I have two 2.5" IDE drives kicking around which I was going to play with, a 512 MB Toshiba and a 1.3 GB Apple-branded IBM. The 512 MB drive works fine, the system starts and can initialize it. With the 1.3 GB drive, which did originally come in my first 1400, the system won't boot at all. If there is no bootable CD in, then I get a weird screen I have never seen before, with text printed way too small to be readable on this LCD screen. Then it throws a "bus error - restart" message. If there is a bootable CD in the drive, then I get a few seconds of happy mac face first, then the weird screen and bus error.
What did I do to the hard drive? A while back I bought an Atari Falcon which came with a funky rubber-coated 512 MB drive which was too small for my needs. Only other HD I had was that 1.3 GB which I had then recently removed from my upgraded 1400. I formatted (with some difficulty) the 1.3 GB to be my Atari drive for a few weeks, which I then replaced with a 4 GB drive I found. I figured that there would be no reason why I couldn't just reformat the 1.3 GB drive to use in a PowerBook later, but it appears I was wrong. I can't reformat it since the system won't even start with it connected.
I am not really looking for any solutions to this one, but it surprised me, so here's FYI.