Some Trojans like to mutilate the Task Manager to make it more difficult to detect and kill them. Suspicions are:

• Windows Update is not running properly.
• You recently opened a bad email attachment.
• You don't have a virus scanner running that is getting daily updates.
• Your computer was or is connected to the Internet without an effective firewall or NAT (Network Address Translation) router.

Of course it could be something else. Try an appropriate Google search.