Here's a quick fix on how to repair this functionality.
Go to Start Button:
Run Command Prompt
Type: regedit
Navigate to:
Hive: HKEY_CURRENT_USER
Key: Software\Microsoft\Windows\CurrentVersion\Policies\System
Name: DisableTaskMgr
Type: REG_DWORD
Value: 1=Enablethis key, that is DISABLE TaskManager
Value: 0=Disable this key, that is Don't Disable, Enable TaskManager
