WD My Book Essential not recognized

Yesterday I purchased a new Macbook Pro running Yosemite 10.10.3.  I have an old (2006) WD 500GB My Book Essential that will not show up when I connect it to the Macbook.  What can I do to correct tthis?  Any suggestions would be greatly appreciated, thanks.

Welcome to the Community.

Is the hard drive detected within your Mac’s built-in Disk Utility diagnostic application? If so, does it allow you to repair the hard drive?

Instructions related to accessing Disk Utility are available in the following link:

http://wdc.custhelp.com/app/answers/detail/a_id/1362/

If it does not show in Disk Utility, does the hard drive still work in older computer systems?