First, check if your host is up, then confirm the database name, user, and...

https://wakelet.com/wake/sdrPiuroqzkIzbmVsD86O

First, check if your host is up, then confirm the database name, user, and password in WordPress. If the error stays, try deeper fixes for bad tables or low server space. Ask your host to review logs if you cannot reach the database or need server access.