Here's a quick jumpstart for you when you are in Hyper-V troubleshooting mode:

Description of the update for the release version of the Hyper-V technology for Windows Server 2008

(950050) - Describes the update to the release version of the Hyper-V technology for Windows Server 2008.
http://support.microsoft.com/kb/950050/en-us

Description of the Windows Vista Service Pack 1 Management Tools update for the release version of Hyper-V

(952627) - Describes the Windows Vista Service Pack 1 Management Tools update package for the release version of Hyper-V.
http://support.microsoft.com/kb/952627/en-us

You are not prompted for credentials after you receive an "Access Denied" error message when you try to connect to a virtual machine from the Windows Server 2008 Hyper-V MMC snap-in

(954279) - Discusses a problem in which you are not prompted for credentials after you receive an "Access Denied" error message when you try to connect to a virtual machine from the Windows Server 2008 Hyper-V MMC snap-in. Provides a resolution.
http://support.microsoft.com/kb/954279/en-us

Increased functionality and virtual machine control in the Windows Server 2008 Failover Cluster Management console for the Hyper-V role

(951308) - Discusses the increased functionality and virtual machine control in the Windows Server 2008 Failover Clustfer Management console for the Hyper-V role.
http://support.microsoft.com/kb/951308/en-us

Event ID: 5936 is recorded when you try to create a new cluster in Windows Server 2008

(947725) - Describes an issue that may occur when the CNO of a destroyed cluster is not successfully removed from Active Directory.
http://support.microsoft.com/kb/947725/en-us

When you try to enable, disable, or update Hyper-V technology, the process stops responding

(950792) - Describes a problem that occurs when you try to enable, disable, or update Hyper-V technology on a Windows Server 2008-based computer. The resolution is to rename the Cpqteam.dll file and then to try again.
http://support.microsoft.com/kb/950792/en-us

Virtual machines that were created on the beta version of the Hyper-V role do not start after the Hyper-V role is updated to a later version

(949222) - Describes an issue in which a virtual machine cannot start. To resolve this issue, you must delete all virtual machines that have the beta version of Hyper-V. Then, re-create the virtual machines.
http://support.microsoft.com/kb/949222/en-us

The NLB host does not converge as expected on Windows Server 2008 Hyper-V virtual machines

(953828) - Fixes a problem that occurs when a Windows Server 2008 virtual machine is running in the Hyper-V environment on a Windows Server 2008 host computer.
http://support.microsoft.com/kb/953828/en-us

Guest operating systems that are supported on a Hyper-V virtual machine

(954958) - Describes the server and client guest operating systems that are supported on a Hyper-V virtual machine that is running on a Windows Server 2008-based computer.
http://support.microsoft.com/kb/954958/en-us

Sleep and hibernate power features are not available when you enable Hyper-V technology on a Windows Server 2008-based portable computer

(954418) - Describes that sleep and hibernate power features are not available when you enable Hyper-V technology on a Windows Server 2008-based portable computer.
http://support.microsoft.com/kb/954418/en-us

Still having trouble? Don't forget to try the Hyper-V forum: http://forums.technet.microsoft.com/en-US/winserverhyperv/threads/