If your Nero program is the only one not working for opening the photos, as compared to something like the built in photo viewer within your operating system, then the program has probably been corrupted somehow. Just my best guess. If you start from the program executable (not right clicking), does PhotoSnap still refuse to open the pictures?
If you have the serial number for your installation of Nero saved somewhere, you can uninstall, run the Nero clean tool for Nero 7 and then reinstall the whole Nero burning suite. That is more or less the nuclear option for solving the issue.