I've seen this on server 2016, where the image I downloaded was incorrect. You'll need to make sure you're downloading just the Server 2016 standard ISO or the datacenter ISO.
If you're using an old OS, or have verified that your ISO's are correct, you may want to try the following:
The link below will get you an ISO. When your building your first image, have two CD Drives, one for the OS image, another for the storage drivers.
Where you see no disks displayed, load the second CD-ROM and inject the storage drivers. You should see your disks.
what I did was I added a second CD-ROM with the VirtIO.iso loaded on it. once I got to the page where I can choose the vDisk to install OS I selected load drivers.
here is a youtube video that outlines the basic steps I took:
Excellent. Thanks for sharing the video, hopefully this helps others with the situation you were in. Don't forget to mark your solution, so the post is marked as resolved.