I have downloaded Mountain Lion but it won't install
I have downloaded Mountain Lion but after I have read the terms of the software license agreement and agreed all I should do next i click on the Macintosh HD and install but everytime I click on Macintosh HD I get a message come up saying. This disk cannot be used to start up your comptuer.
Why can't I install
iPhoto '11, Mac OS X (10.6.8)