When you start the Disk Defragmenter utility in Windows 8 or 10, the following error occurs and the Disk Defragmenter window doesn’t open.
Storage optimization cannot start because the task scheduler service is not running. Start the task scheduler service and try again.
Just as the error message instructs, starting Task Scheduler resolves the problem. Use these steps:
1. Click Start, type Services.msc and press ENTER
2. Double-click Task Scheduler service from the list.
3. Verify if the service is started and the startup type set to Automatic.
4. If it’s not started, click the Start button to start the service.
If the startup type is set to anything other than Automatic, such as Manual or Disabled, and the option is grayed out (it would be grayed out by default, unless you’re viewing it under SYSTEM account), download Scheduler.reg referenced in article Task Scheduler Service Grayed Out in Services MMC and run it.
The REG file should set the Task Scheduler service startup type to Automatic, and you may have to restart Windows to check if Task Scheduler starts automatically the next time onwards. The REG file can be used for Windows, 7, 8 and 10.
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Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in Windows — delivering support for Microsoft's consumer products. He has been a Microsoft MVP (2003-2012) who contributes to various Windows support forums.