Added photos to a new album, now all photos except for 1 are gone

I had recently imported and added photos (3000+) to a new album on lightroom on my macbook and had started to do a selection but did not finish.

A few days later I want to continue my selection work, but all photos have disappeared except for 1.

In the meanwhile I had already formatted my sd card so I have no physical copy left anymore.

Please help as its a paid assignment.