Getting to the AmigaDOS window means that you created a boot partition with the highest boot priority which does not have Workbench installed on it. Enter CD command to see which partition you are on and either use HDToolbox to change the bootpriority to be lower than your desired boot partition or install AmigaOS onto this partition.
If this only happens on a warm reboot, you probably have multiple hard drives and the one your boot partition is on does spin down upon reset and does not spin up again quick enough for AmigaOS to recognise it. Either swap the drives or move your boot partition to the remaining drive.
In general you should not mark a partition as bootable if you don't plan to install AmigaOS on it. In the worst case, if no boot partition remains, you get the insert-disk animation.
Bye,
Thomas
