@melott-
Hmm... I never had good luck with the 3640 board in an A3000. But, I was attempting to install it into a very old 3000, also. (early softkick 1.4 machine that I had upgraded to 3.1 roms) I never could get it to run stable, and most of the time it would hang in startup or earlier. There are other things that need to be upgraded in an early 3000 for it to be able to take advantage of the 3640. (Buster, DMAC and Ramsey, if I remember right.)
The hard drive that goes missing -- Personally, I'd check your internal ribbon cable, and make sure it's intact and doesn't have any breaks or bad connections. Also, make sure you don't have anything grounding / shorting against the bottom of your hard drive.
@herewegoagain -
Well... It sounds like you know the drill... Remove everything from the 3000 (zorro cards, etc) and try to boot it clean with a minimal setup, and then start adding back from there. I had a zorro network card (x-surf, if it matters) fail in a 4000 that caused a very similiar set of error conditions. Hopefully it's just an accessory that has died, and your miggy itself is ok.
