Macbook pro retina 15 inch will not recongize WD30ezrx hardrive external

Hey guys and gals hope you can help me out on this one. I have the wd30ezrx hardrive in an external enclosure. the power light on the enclosure comes on and if i reboot my mac the little blip from teh harddrive happens. however the macbook pro cannot see the hard drive. cannot se it in finder or diskutitlity or about this mac.

any ideas?