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Win+R and type "powershell" to open PowerShell. If you're using Windows 10 and the taskbar won't stay hidden, you can try using the PowerShell utility to fix it. Confirm that you want to proceed. This will open a new "Administrator" PowerShell window. Make sure you paste it into the "Administrator" window: Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"} You may see a few errors as the command runs, which can safely be ignored. You should notice that the taskbar hides as it should and stays hidden.
Press . Right-click the PowerShell icon in your taskbar and select "Run as administrator." Copy and paste the following command. Run the command. Click or tap the Start menu after the command finishes.