Hi,
Sorry, i didn't express my self clear. After you convert your old pc, edit it's configurarion from the Virtual machine menu. This should be done before you turn on your virtual machine.
It's not disabeling the devices from windows in which case you do will have to turn the vm on, it's "disconnecting" the actual virtual devices fram the virtual machine.
Hope this helped you Image may be NSFW.
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Regards,
Seb