I had to reinstall Mountain Lion from the disk utility because my macbook pro would not boot. After the reinstall, iPhoto and several of my apps will not start. What can I do?
Have you logged into Software Update or the Mac App Store, using your Apple ID and password? Have you gone to System Preferences: Internet & Wireless: iCloud, and logged into iCloud with your Apple ID and password?
Try these things and then see if you can launch those apps.
...in addition to Wheat's suggestions, make sure you are running the must current builds of Mac OS and iApps (via Software Update).
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