Enable Task Manager the Windows XP

If a computer administrator has disabled Task Manager in your user account, you’ll see the message Task Manager has been disabled by your administrator when you try to start Task Manager. If you are an administrator, and the restriction wasn’t intentional, you can reactivate Task Manager through the registry.

Here’s how:

Never experiment with the registry settings. Back up the registry before making any changes.

Click the Start button, and choose Run, or press Start+R.
In the left column, navigate to the following key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\ CurrentVersion\Policies\System The key is only available on systems where Task Manager has been disabled through Group Policy.
In the right pane, double-click DisableTaskMgr, and set its data value to 0.
Exit the Registry Editor.