gone like a bubble…

Well this happened before, and I’ve no idea how it happened again. Yesterday it worked fine, but now it’s just GONE! As in “Cannot Find Server” gone. When I went to my WP Admin, it says something like “Database out-of-date. Please upgrade.” Then when I click upgrade, and upgraded wp, it still doesn’t work… What does this mean? I installed WP again using another database now… But what if it happens again? What should I do?