Hyper V diffdisk VM starts and stuck on black screen, blinking cursor

[markgsus.work]

Hi all,

I am totally stumped by this and have done this many times. I create a parent disk (Windows 10 build 1607, have to use this old build for testing purposes) and then a differencing disk using Hyper V using methods such as desribed here:

https://msitpros.com/?p=3735

https://www.altaro.com/hyper-v/hyper-v-differencing-disks-explained/

When I start the diff disk vm for the first time I get a black screen with blinking cursor.

In desperation I tried this

http://www.etdot.com/2012/02/29/felipe-binottos-blog-windows-wont-boot-black-screen-with-blinking-cursor-at-the-corner/

and it seems that no C drive is available when I go to the command prompt. This sound like it would be part of the problem (obviously).

Any ideas why this would happen? I have googled around and people have various problems with starting the vm and hitting a black screen but none of them work for me.

FYI trying to debug the issue in any way I could I found that pressing F8 (after adding the hyper v delay) during boot does not get me to any BIOS menu.

Thank you for any help
m

 

[markgsus.work]

For anyone who has a similar issue in the future I describe what worked, though I don't know why.

I was creating my parent disk on an UN-PATCHED (i.e. no updates applied) version of Win10 1607.

Recently I applied all patches (as of 28 September) to the parent disk (Windows 1607), sysprepp-ed it and created a new child diff disk: this worked.

I guess something in one of the patches must have fixed the issue? I don't really know.

m