I think I've cracked it! In the FAQ (thanks Tony!) I found that you can start the player with -i to make it not read the current playlist. It was enough to do that once, now it boots again. The first thing I'm going to do is make a backup of the disks now...

Is there a way of obtaining a new IDE cable, other than through Rob? I suspect that a bad cable caused the problem in the first place so I want to replace it as soon as possible.