Have you ever installed AND registered it? The serial numbers of my registered SCS software are still on www.sonycreativesoftware.com (My Account > My Software). If you ever registered the S/N should/may be on your MAGIX My Account / My Products as well https://www.magix.com/us/support/my-service-center/.

If there isn't a crucial reason for you to have that old version, I suggest you try to find offers for a newer version. Vegas Pro and Movie Studio vs. 6 are from 2006.