The fact that the device is not recognized by Disk Management but it is by Device Manager, could indicate that only the enclosure is recognized but not the HDD inside.
If we assume that the cable is working fine (I do believe it would be nice to try another cable), this could be caused by faulty enclosure or a dead drive. In both cases, you have a couple of options:
- Look for some professional help, in case the data is really important.
- Contact the place you got the drive from or our Support and RMA it:
http://products.wdc.com/support/kb.ashx?id=wWQIzw
In the second case, you will not get your data back though.
Let me know in case you have some more questions,
D_Know_WD