Mac Suddenly can't My Book World

I recently brought a My Book World.  When I first got it, I couldn’t see the drives in Finder.  I had to use a windows PC to set up the drive before finder could see it.  All has been working fine for two weeks including Time Machine Back ups.

Yesterday, turned on the MAC and I couldn’t see the two network shares.

Now the only way I can get to the drive is to connect server via finder manually and enter it’s IP address.  I can see the files but can’t get the correct network shares so Time Machine can work.

To be honest it been flakey from day one and some times it doesn’t see it in windows either.

Any suggestions where to start looking for what is wrong. 

First thing to do is narrow down where the problem is. Can you access it from the PC? Have you tried replacing the ethernet cables (both on the mac and the NAS)?