When you first setup you're system you would have associated the system with an Apple ID and that Apple ID is the one needed to re-install the OS or the Apps that came installed on it.
When you log in with the Apple Id you are using do you see Mountain Lion being listed as purchased?
To reveal purchases if you had hide them, you need to go to the account page in the MAS. From the Featured screen look for the Quick Links and in there is a link to your account.
If Apple recommended re-installing the OS then you should probably follow their advice, though I'm not sure why that will help in this situation. Doing a re-install of the OS isn;t to bad just be sure not to do a clean install as that will wipe out your HD first.
If iPhoto was "pre-installed" on your computer at purchase, then this computer must have been purchased before July 20th 2011. After July 2011, computers did not come with it pre-installed. You got a free copy of it, but you needed to download this free copy from the App's store.
If it was pre-installed, then you need to locate the install disks that came with your computer. They would have a copy the original version of iPhoto, that came with your computer.
You need to completely delete iPhoto from your computer, before you re-install it. Your pictures are not in the Application, so un-installing it, will not loose any of your pictures. To uninstall it, do the following:
- click finder in the dock, so the word finder appears beside the apple. Also note in the top menu, is the word "Go", click the go menu and select:
- computer / Mac HD / applications - drag iPhoto to the trash
(You may not the next two items, but you need to check, because if you do, they need to be deleted) Go back one screen by clicking the backward arrow and then select the "Library" folder, then the receipts folder. Look for "iPhoto.pkg" and drag it to the trash.
Go back one screen by clicking the backward arrow and then select the "Application Support" folder. Look for a blue folder entitled "iPhoto" and drag it to the trash
Close all open windows, and insert your "Mac OS X Application" install disk into your computer. Select "bundled software" and follow the on-screen instructions by selecting "continue" until you get to a screen with an "Install" button on it. DO NOT click "install". Select "customize". Check off only iPhoto, then install.
Once the installation is complete, you need to do software updates to update iPhoto to it's maximum version. Once it is updated, you should be able to launch iPhoto.