Why won't my back/forward buttons work? Also my history and bookmarks are gone. Nothing that has already been suggested on this site has worked.

Today when I logged my computer on my bookmarks and history had vanished. I then noticed my back and forward/buttons had stopped working as well. I have tried several of the suggestions on this site, but it is hard, because I can't go back pages, I have to close everything down and start over (did I mention that sometimes everything stops working?) I just want my bookmarks back. How can I get them?