If you get error message "Disk defragmenter cannnot start because the task scheduler service is not running. Start the task scheduler service and try again." when opening disk defragmenter on windows 7, try this to solve it:
1.Open Start>>Search>>services.msc
2.Check windows event log, make it enable, automatic, and then start it
3.Check task scheduler, make it enable, automatic, and then start it
Hope this helpfull ^^