If your device is powered on but show up as Offline under Menu ➝ Devices your device probably blocks ping attempts.
On Windows, follow these steps to remedy the issue:
Change from Public to Private network
Go to Settings ➝ Network and Internet ➝ Change connection properties
Change Network profile from Public to Private
Open Search bar on Windows (Windows-key)
Search for HomeGroup
Press Change advanced sharing settings...
Under File and printer sharing, check the option Turn on file and printer sharing
Press Save changes
You should now be able to see your device as Online.