Could you please check whether you are working on correct catalog or not.
It's possible that you may have inadvertently created a new catalog. In Lightroom, go to File->Open Recent and see if there is another catalog you can select. If that isn't the problem what has happened that makes you think all of your work is gone?
The recent catalog is the one that is open right now. When I open lightroom its like I just ordered it and haven't uploaded any pictures. There is nothing on it.
If you have not change the default location of Lightroom catalog then you can find it under the Pictures in a folder name Lightroom or you can look for a file with extension .lrcat in your system.