If this is a recent occurrence then try fixing things via System Restore, or use the System File Checker.
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista (or 7, or 8).
http://support.microsoft.com/kb/936212/#appliesto
See, Control Panel\All Control Panel Items\Recovery\ Open System Restore
Use the System File Checker tool to repair missing or corrupted system files
https://support.microsoft.com/en-au/kb/929833
How to analyze the log file entries that the Microsoft Windows Resource Checker (SFC.exe) program generates in Windows Vista
http://support.microsoft.com/kb/928228#appliesto
See, Control Panel\All Control Panel Items\Programs and Features\Turn Windows features on or off.
You could try unchecking Hyper-V via Control Panel/ Programs and Features/ Turn Windows Features on or off/ Hyper-V. This will uninstall it. You then reboot and then reverse the steps to reinstall it. Keep any .vhd files that you require safe, it is
only the VM Machine that is uninstalled and then reinstalled by the process.