Upon migrating a Vista or 2008 virtual machine from Virtual PC 2007 to Hyper-V, the Hyper-V Integration Services sometimes look like they are not working at all. A warning also pops up when attempting to reinstall them:
A previous installation of Hyper-V integration services has been detected. Click OK to upgrade to repair this installation.
If they are installed, then why aren’t they working? The most common reason for this is that HAL detection (a Vista/2008 specific feature) is disabled, while Hyper-V Integration Services require them to function properly.
To enable this feature :