All the drives that work in the PC power up in the A1200, but the A1200 still waits the 30s and shows the insert floppy screen. This happens if the IDE buffer is connected or I'm using a 2.52-3" cable. All the cables are fine, I've even used the cables from the PC aswell with no luck.
But have you used any hdtools software from WB and see if they show up there? I think it is perfectly normal that the purple screen remains if there is no bootable amiga partition i dont think it even shows up in the early boot screen if the HD's lack a amiga partition.
