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Sometimes application are still running on background, not visible to users, you need to close them using "Windows Task Manager"
To close such programs use the Windows Task Manager. To start Task Manager, take any of the following actions:
Once the Task Manager is running, select the Processes tab. On older Windows version you may need to click on the Process Name or Image Name header to sort the process names.
Now right-click on every process that the Flash Player installer needs to close (e.g. iexplore.exe), then select End Process.