I'm on a Mac and I lost my catalog although I can see all the folders if I want to re-import each and every one. What happened and is there an easier way to fix this problem? PS and Bridge work fine. the images are all there. Just then catalog simply disappeared. I'm using LR CC
First check the menu:/file/open-recent/ list to see if you just opened a new or different catalog by mistake.
Next search your hard drive for all the "*.lrcat" files to see if your old catalog is still around.
Also check your "trash can" or "recycle bin" in case you deleted it by mistake.