After using my Lightroom 6 (upgrade) for several months up till this morning (37000 images), I open up Lightroom to be faced with a completely blank version, no photos, nothing! Adobe seems to think I am a new user?! I am in total panic. What could have happened?
Open LR , click on file open recent and look for the catalogs, one of them has to be the recent one on which you were working in the first place.
This happened to a friend of mine and it turned out a family member had logged him out and had logged onto another account on the computer without logging out afterwards. Of course they should have been using passwords on their screen savers but my fried didn't notice and thought his Lightroom had completely been obliterated. Check whether it is not something simple like that. Make sure to log onto your own account and not a guest account. Do the things Rohit suggests if you're logged onto your own account And you don't see your main catalog.