I feel your pain. Where as my A4000 problems aren't as bad as yours, I too have a non fully functional motherboard. For the IDE issue, you can always get an IDE Zorro II or III card and use that, they might be slightly faster, and for the power supply there is a gentleman here who makes ATX converters so as to allow a newer power supply to be used. I don't remember his screen name unfortunately, but he usually ends his posts with his real name with is Nathan, just like me. The Fan should be the easiest I would think. Identify the fan size (usually in mm)then see if you can find a replacement with the correct power connector. Sorry if I'm not much of a help, but I wish you the best of luck with getting your A4000 back up and running.
*edit* - Sorry didn't read as closely as I should have for the IDE whether or not it can be repaired I am not certain. I thought one of the Chips on the board ran that, but again, I am not certain on that. Others will know more than me.