If you are only seeing “music”, “video” and “photos” folders that sounds like you are accessing the My Cloud Twonky DLNA media server and not the file server side of the My Cloud.
Look for this MyCloud icon in Windows File Explorer under Network:
NOT this MyCloud icon in Windows File Explorer:
If you are not seeing the correct icon in Windows File Explorer then it is worth checking to ensure Windows 10 is properly configured. Some suggestions on things to check are detailed in the following post:
In particular see Windows 10 Specific Method 1 through Windows 10 Specific Method 5.
