Baby steps:
1- Boot the Amiga with the Workbench system disk (main disk).
2- Hold the right mouse button and in the menu select "run";
3- In the freshly appeared window, type "newshell" (no quotes);
4- In the AmigaDOS prompt, type in "info". This will show all devices in your machine. There you'll find the correct device to type in the toolbox of the icon of hdtoolbox.
5- With the edited hdtoolbox (or in the shell, type "hdtoolbox nameOfTheController.device"), try to partition the drive again. After the partition job, all the partition icons will show on the main screen with some like DH1:

?? or DHx:NDOS. BTW: the
system partition must be set as "bootable";
6- Left click on a partition icon and then right click, go in icons:format;
7- Repeat the process 6 until all partitions are formatted;
8- After this process, reboot and put the install floppy on the drive.