Lightroom: my photos are desappearing!!

Hello community, 

i'm using lightroom everyday and i always do by myself the backup of all photos.
i never used the automatic backup because of i've never found the choise about the saving options like "raw+mod" or "tiff" etc..

but anyway, the problem:
yesterday night i tried to put on the option of automatic saving of backup. the program restarted.. and then, when it was opened again, the page was very little and to the top left of my desktop (my pc was going crash, i think). when i finally opened in view "full screen",  i've seen that lightroom were deleting all my photos in front of my eyes!!!!!!!!! 
but my trash is empty... so,  my photos are not deleted, but DESAPPEARED!!
naturally i restarted lightroom and put off the automatic saving again (thinking that was this the problem) but my photos continued to desappear so i closed again the app and tried again. 
NOW: 

1) from the 2800 ph that i had, now i have only 1300 ph in the program.  photos that are not saved anywhere with my modification because of in the last month for the first time i didnt have the time for doin my backup (that's why i was trying to use the automatic backup!!). 

2) everytime i open the app of lightroom, other hudreds of photos desappear in a few second 

please someone can help me?! the photos were for a competition, i worked so much on them and now i lost everything!!!! 

Ps. i naturally work with raw files (i have all of them, i just need back my photos with the modification and they were only in my lightroom albums!!!) 

NB. i work with lightroom and not with lightroom classic 

thank you 

F.D.