Trying to download OS X mtn lion on Mac book pro running OS X 10.6.8 and it won't download. Advice?

I Have been trying to down load the OS X mountain lion from the App Store onto a Mac book pro running OS X 10.6.8 with no luck. The store has charged my credit card for the purchase but I have no upgrade in my system. When I click on the download button, the lion icon pops into the dock. If I put cursor over the icon in the dock, it shows "OS x mountain lion......waiting" and never gets beyond that. What am I doing wrong? Thanks in advance for your guidance.