no thumbnail

[AC Question]

i have couple weeks used alcatel one touch pixi 3. the ok button on viber and google hangouts for taking pictures (photo message) doesn't react. camera works. tried to fix the problem, but i made it worse. don't know what i did, but, after i take a pic there is black no thumbnail in gallery. tried to clear data in media storage, waited and did reboot, still nothing. backed up photos in dropbox. root explorer is buyable, and thats a no option for me. tried to connect phone with android photo recovery (dont know why really, i backed up all in dropbox), in connection process phone crashed. previously did wipe junk files with clean master, think i deleted that default thumbnails. clear data-reboot didnt help for it to come back. phone started reboot by itself couple times. one time it was black screen cause i pulled it out of pc without eject media cause it coudlnt be done actually.......how can i again take pics and reactivate that ok button in viber and google hangouts, and fix the no thumbnails problem in gallery ? thnx for answer, never did this before.