Install Windows Server 2008 Core on a Dell Optiplex 790

Does anybody have experience installing Windows Server 2008 Core on a Dell Optiplex 790? When I connect to the machine with the Hyper-V Manager Administrator snap-in, and try to create and run a virtual machine, I get the error "The Virtual Machine could not be started because the hypervisor is not running". I've disabled the Execute Disable functionality in the BIOS as was requried for other Dell models, but no matter what combination of security and virtualization settings I use on the machine, I can't get this working.

EDIT: I've installed Windows Server 2008 Core on a Dell Optiplex 790, and I'm trying to install and setup a guest VM on the Hypervisor

EDIT 2: The Hyper-V role is installed and configured, without any errors in the event log. Hardware-assisted virtualization is also enabled.

I had the same problem on HP machine with VMware. First try to uninstall Hyper-V, then enable Virtualization and Data Execution Prevention in the BIOS and after that install Hyper-V again.

Aditional information: Here I have found some article, with almost the same solution: http://reidablog.blogspot.com/2008/06/with-correct-bios-settings-enabled-on.html

Good luck!