I recently updated from LR 4.0 to LR 6.0. The update posted a new icon on my desktop and renamed the catalog by incrementing it to 2carta. Everything was working fine. Then 2 weeks later I updated my windows program from 8.1 to 10. During the update the windows program informed me that it had identified a LR program that needed to be updated to 6.0 and asked me if I wanted to do this. I said yes. Windows then posted a new LR icon on my desktop. However, when I click on this icon the catalog that comes up is incorrect. How do I find the prior catalog that I was using before I updated windows? Isn't it stored somewhere on my "C" drive? I am a PC user.
Your Lightroom 3 catalogs are located in Pictures/Lightroom Folder by default.
You can try opening them and use the correct upgraded catalog in Lightroom 6.(check the Lightroom version should be version 6 under Help>>About Photoshop Lightroom)
Hope that helps.