Windows suddenly cannot see my WD NAS by name anymore

I have had this WD PR4100 for a while now and it has a network name of sonya
So I can get to it from my Windows 7 box in the usual way \SONYA
I also have three network drives mapped to it: videos \SONYA\Public(X:)photos and so on.
In the last week or so I have not been able to get to it by network name, only by IP address.
It still has its name, and other devices on the network can see it okay, such as my phone and tablet and Macbook.
The Asus router can see it okay as well, so this has to be some kind of Windows problem right?
Restarted the WIn box, and the router, and the NAS.
What next? Anyone else had this?

Hi ixnay,

Please check the link, it may help you: