What are you trying to do? Accessing http://MyCloud.com is generally for remote access. Accessing http://wdmycloud.local if using a Macintosh or http://wdmycloud if using Windows will bring up the My Cloud Dashboard.
It is probably advisable to read the My Cloud User Manual (http://www.wdc.com/wdproducts/library/?id=439&type=25) to learn how to access the My Cloud and use it’s various features including how to “map” the My Cloud to your Macintosh computer for easy access. Or see the following WD Support link for general directions on mapping the My Cloud to the Mac.
On the Mac one can connect to the My Cloud by doing “Command+K” which opens a dialog box that will allow you to connect to a “Server” (which is the My Cloud). In the Connect to Server, Server Address field try one of the following to connect to the My Cloud.
Or see the following web link for general steps: