I upgraded my desktop to windows 10 a few days ago. After the update I signed into my microsoft account and everything was all upgraded. I added about 2500 files to lightroom and then I used the mobile sync. I backed up my images to one drive and closed lightroom. A few days later, I turned on my desktop and it says that my PC has fully upgraded and gave a tutorial and all the new features. After that everything was back to normal and I opened up lightroom to find all my images were gone. I tried to find the catalog but it did not exsist anywhere. I also tried to look through the recent catalogs and nothing showed up. Where did all my images go? They are also not on my tablet?
Search on your machine for .lrcat files which would list all the Lightroom Catalogs that you have.
Also, look for the backup catalogs if you backed it up after using last time.
By default, backups are located under Pictures\Lightroom\Backups