I’ve got three barebones, configured as high-performance PCs at the office. The usage of these PCs was decided to be Hyper-V servers, which test team would setup and use for their dark matters.
All that was great, with the exception of one: No virtual machine could successfully start! We successfully installed and configured Hyper-V Servers, but then any virtual machine, doesn’t matter imported or new, would fail startup with the dreadfull message “<virtual machine name> could not initialize”. Very helpful, as you can imagine.
I contacted my best source for any virtualization issue whatsoever: Alex Miloev! The situation became even darker, as he was not able at the moment to help deeper, and I exhausted more or less any “simple” fix I could imagine. Solutions from the newsgroups suggested what I already did (stuff like “turn on your processor virtualization flag”, Doh!).
I was desperate to the degree, where I started looking for and downloading VMWare ESXi 5.0. Knowing what risky business this is, I guess you do understand my desperation 
.
The thing, whcih did it, I found almost by accident. This very interesting hotfix You cannot start virtual machines on a computer that is running Windows Server 2008 R2 and on which a CPU is installed that supports the AVX feature did the charm. I was not initially sure, since I did not know / I was not able to check if my disks were of this kind, but I decided to try it.
And the miracle happened! All worked like a charm! First on one of the machines: all was OK. Then the other two – just installation of the fix itself removed the obstacle and all VMs started normally!
Microsoft, however, offered very weird way of delivering the hotfix! I never received hotfix download link by e-mail, I guess this is something of the new stuff, which Microsoft constantly tries to change (actually, to make it better, but it’s not always better). Nevermind that, the hotfix link came, it worked and now my machines are working like a charm.