Which WD backup system are you using? SmartWare? Sync? You will have to configure it to choose what folders are backup up to the MyCloud, and how. To be honest, it sounds like your backup/copy tool isn’t configured correctly.
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=3828
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=11395
I am struggling to identify from your description what software you are using to access the MyCloud; the WD Desktop App, perhaps? Does it look like this:
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=10480
If you are using a Windows PC, I would suggest you open ‘Computer’, then select ‘Network’, and the MyCloud should be present as a network device. You should be able to double-click on that to open the files, and use Windows File Explorer to view them.
It should be noted that you don’t need any WD software to access the Mycloud; you can access it via your normal file manager (e.g. Windows File Explorer).
If you haven’t read the User Manual, it would be a good idea to take some time to read it and understand how the device works, and how best to access it.
http://www.wdc.com/wdproducts/library/?id=439&type=25
The first few articles here are also very useful:
http://support.wdc.com/product.aspx?ID=904&lang=en
especially:
http://support.wdc.com/KnowledgeBase/answer.aspx?ID=2676
I’m not sure I understand what you mean here: do you mean that ‘Music’ isn’t music media files (mp3, flac, aac, etc)?