New MacbookPro w/Mountain Lion. Can't see external HD

I just bought a new MacBookPro and it cam with Mountain Lion.

I have an external HD and was working fine, then I ejected it, pluged it back into my iMac with Lion, and it can't be found. I tried on my new MBPro, and same thing... can't be found.

Opened disc utility and it's there. Right clicked on the "missing" hard drive and selected OPEN (see attached image).

As you can see, the missing hard drive is now available, but it won't let me find it unless I go through disc utility. What's up? and how do I fix this?

Thank you,

Tony