Hi and welcome,
I don’t think, the Cubase installation to a specific folder would fix this issue. The installation itself has nothing to do with activation or registration. Start eLCC application (the best was as an administrator) and click to Maintenance. Let the process finished. Then double-check, you can see your USB-eLicenser with your Cubase 5 license in the list. If yes, use the “Registration > Register all eLicenser at MySteinberg…” menu option. The USB-eLicenser will be registered. Now you can use the upgrade Activation Code, to activate your license.
If you need Cubase 5 installer anyway, get back to me, I will send you the link.
Once you upgrade your Cubase 5 license to Cubase Pro 10 license, you will not own Cubase 5 license anymore. You will be owner of Cubase Pro 10 license. But, with Cubase Pro 10 license, you can start Cubase 5. You can also open Cubase 5 projects in Cubase Pro 10 (if you were using 64-bit version of Cubase 5 and 6-bit plug-ins and all plug-ins are still compatible with Cubase Pro 10).