Hmm. 60GB, both disks present.

So, I've discovered that it appears to be the motherboard end. With the carriage out, if I push lightly on that end, it finds both disks, and will continue to do so. As soon as I try to put the carriage back in, just the slight flexing of the cable seems to unseat that connectot enough to cause the problem.

At least I can download the new kernel though, and do some investigation.