This can't happen all of a sudden without changing anything. Did you upgrade, move db or anything similar recently? You should check the db connection and the server logs of confluence when starting. This is not enough information to give any solid answer to.
Check out this document:
There is a config file under home directory: <confluence_home>/confluence.cfg.xml
You can find the home directory here:
confluence/WEB-INF/classes/confluence-init.properties ("confluence" being your installation directory)
Check out the db config file and see if it points to the right db.
And one more point to notice here is,
If you have backup of your confluence, you can test it first whether it is working fine.
Hi Community! We're thrilled to share that Team Calendars for Confluence is now a built-in feature for Confluence Data Center releases 7.11 and beyond. A long time favorite, Team Cale...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events