Do you have the Aperture 2 or 3 version? And has it ever been updated via Software Update? If so, can you post exactly which version you have (to do that, open the Applications folder in column view, highlight Aperture, and in the right column it should show you the version number. I also purchased my copy of Aperture via install DVD, but I updated it and did associate it with the app store, so it provided a notice to download the latest version before it was discontinued.
You can try to install from your DVD if it is v. 3.x; I did the last install in Mavericks (10.9.x) and have not tried a fresh install in Yosemite. The worst that can happen is: you install it (don't try to open it) and then go to the app store and check Updates, and it won't show any. Nothing wasted but a little time.
Once you try all the suggestions here, post back with any results and we can see if your question should be moved to the Photos forum or if you were able to find your pictures...