Click Start--Run--type "services.msc" (without quotes)--click OK--right-click Task Scheduler--click properties--make sure that Startup type is "Automatic" and that Service status is "Started" (if it is started, stop the service, save changes, reboot, restart this service).
If the above doesn't work, suspect malware. Reboot into Safe Mode, scan for Spyware and Viruses (make sure scanners are up-to-date first), deleting any found. Rescan to make sure no problems are found on second scan.
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