my app store file is damaged/incomplete

This is incredibly frustrating.

I'm not that attentive to the new innovations that Apple provides in the software updates, but I found out today, in attempting to upgrade my OS to Yosemite that I was supposed to have received the Mac App Store in previous software updates. I'm running 10.6.8, and my software update is telling me there are no further updates as my computer is all up to date.

But I don't have the Mac App Store anywhere on my computer. In searching my applications, I find one titled "App Store" with a blank application icon with a NO sign overtop (as in the same logo that goes over a cigarette for NO SMOKING" signs.) When I click on this it says, "You can't open the application App Store because it may be damaged or incomplete."

I'm trying to upgrade my OS so I can get the new version of Itunes so I can restore my ipod so I can listen to music. Every single step in trying to reach that end has been a pitfall and this is one of the most frustrating. I'm ready to upgrade, I've backed up my computer, and now I can't even download the OS upgrade... Nobody else seems to have experienced this. Somebody PLEASE HELP ME.