Samsung tablet reset on its own not sure how?

I have had my tablet for i think 2 yrs and have never had a problem. Used it everyday. Then I put it up for the weekend got it back out Monday 3/26/2018 was watching a tv show I had (app downloaded) had to stop closed the cover on tablet. Then today 3/28/2018 I get it out to finish show and it has reset all my apps pictures gone. Not sure how to get anything back. Not sure why or how this happened. Is there anything I can do to get pics back that's all I care about. Thank you

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