“visit site” problem

I have a problem now. 5 minutes ago I was working on my site and it was working properly. Then I added a new user for trial, then I came back to my admin accunt. But I saw that everything is gone. all my pages, links, added themes gone!!! I will get crazzy please help me as soon as possible!! When I click on “visit site” it returns to wp-admin and dashboard. What can I do?