This happens because the Windows Operating System does not have the appropriate drivers (VirtIO driver) to read the disk that has the operating system installed on it.  

In a nutshell:

1- Download both VIrtIO and Windows ISO to the image store in the cluster (you can use prism “image configuration” or prism central Explore->images->add image”)

2- Mount both VirtIO drivers and Windows ISO as CDROMs for the guest VM with problem.

3- Power on the guest VM booting from Windows ISO CDROM, you will see an option called “Troubleshoot”

4- Choose the above option and go to command prompt

5- Get the list of mounted disk drives and navigate tot eh drive where VirtIO resides

7- Load the drivers: “drvload vioscsi.inf”

8- see that drivers are mounted now “wmic logicaldisk get caption”

9- exit and reboot guest Vm

10 After you login, go ahead and install the VirtIO MSI package

For more details please see:

https://portal.nutanix.com/#/page/kbs/details?targetId=kA00e000000kAWeCAM