Hi there King855,
Sorry that you are facing some issues with your drive.
Is this a new drive? In case it is, there is a possibility that it's file format is supported by Windows but not Mac.
You can just reformat the drive(data destructive) the following way:
http://products.wdc.com/support/kb.ashx?id=cCBvEr
Hope this will help,
D_Know_WD