Contact Apple for a replacement serial number:
Any way to access images?
Without your serial number you will not be able to launch Aperture. You should still be able to see the images in the Media Browser in the iApplications, in Mail, etc. The "Photos" view in the "Media" section of the file chooser dialog in "Preview" will let you browse your Aperture library. You can access the previews this way. For example in Preview (your screen will look slightly differently - this screenshot is from 10.8.2). But the Finder sidebar should show the Media section in a similar way.
To access the original master image files, ope the Aperture library package - ctrl click the library in the Finder, select "Show Package Contents". Your original iages are in the "Masters" folder. Browse and copy, but don't modify anything inside.