WD External HD wont turn on

Hi I have same problem.  2 TB My Book Studio.  Has worked perfectly for months even after installed Mountain Lion.  I disconnected teh drive when I went on holidays.  Now when I plug it in it is just not recognised by my iMac.  No light, no noise and not showing in Finder.  Time capsule says it cant find it.

It is, however recognised by my Macbook Pro.

What is the disc management window?