HT1338 when my apple macpro ret sc conneted to tv by hd cable its not showing, why?

Question

when my apple macpro ret sc conneted to tv by hd cable its not showing, why?

Answer 1

Ok thank you so much, for your timely response.
RESPONSES:
1)   When I set up my iMac, I did not transfer any data directly from my windows PC.  I simply used the same iTunes login and account.  I have access to all of the files via the "Purchased" section of the iTunes store.  If I click "Download Previous Purchases"  text, I can download ALL of the purchases I have ever made.
2)   I have the Apple TV 2, so good news, question answered.  I thought maybe it was the Apple TV 1, but it is the Black model, so bam.  Good response for you.  Well the whole damned reply is an awesome response, just pointing out that one piece of awesome.  I stated that it was an Apple TV 2, and yet you were still good enough to figure I could be mistaken, and provide me with knowleedge just incase.
QUESTIONS:
3)   So can my iMac not stream the data directly from itunes, without download?  Apple TV can, but perhaps that is something among many things that maker it unique, and awesome.
SERIOUSLY.... THANK YOU... 
I work in the computer support section for the Military.  The only problem is we use Windows , lol.  Well that and i've been gone for nearly 6 months on recover.  I go back next month though I hope.  But working in that field gives me the abilty to judge responses that run inside the same vein.  Your response was so awesome that I half thought I might have written it myself.