EDIT: Ignore the CS4231. Sod that.. this would be a problem also, but I dunno if it affects the IDE controller or not.

Check the hard disk cables -- make sure they are actually still connected. Listen for the drive: it should make clicking noises at startup, and you should also be able to clearly hear it spinning after power-on.

Next up is the infamous IDE header on the main board: they used surface mount rather than through-hole pins, and the result is that they tend to come off the pads after a while and may require resoldering.

Cheers