Sql server stopped

1. Ping the server and check the status

2. Check whether services are running well - services.msc

3. Make sure the TCP end points are configured properly 

4. Firewall could be one of the reasons.

5. Check with the authentication & user privileges.

6. Restart the instance after confirming the Trace Flags.-t3608 (optional)

7. This can have many reasons and right reason can be found only when we look into Event viewer and what has caused SQL Server down.  

SQL_Login_Expired_script (T-SQL Script to find When will a SQL login password expire?)

-- When will a SQL login password expire?

SELECT SL.name AS LoginName
      ,LOGINPROPERTY (SL.name, 'PasswordLastSetTime') AS PasswordLastSetTime
      ,LOGINPROPERTY (SL.name, 'DaysUntilExpiration') AS DaysUntilExpiration
        ,DATEADD(dd, CONVERT(int, LOGINPROPERTY (SL.name, 'DaysUntilExpiration'))
                   , CONVERT(datetime, LOGINPROPERTY (SL.name, 'PasswordLastSetTime'))) AS PasswordExpiration
      ,SL.is_policy_checked AS IsPolicyChecked
      ,LOGINPROPERTY (SL.name, 'IsExpired') AS IsExpired
      ,LOGINPROPERTY (SL.name, 'IsMustChange') AS IsMustChange
      ,LOGINPROPERTY (SL.name, 'IsLocked') AS IsLocked
      ,LOGINPROPERTY (SL.name, 'LockoutTime') AS LockoutTime
      ,LOGINPROPERTY (SL.name, 'BadPasswordCount') AS BadPasswordCount
      ,LOGINPROPERTY (SL.name, 'BadPasswordTime') AS BadPasswordTime
      ,LOGINPROPERTY (SL.name, 'HistoryLength') AS HistoryLength
FROM sys.sql_logins AS SL
WHERE is_expiration_checked = 1
ORDER BY LOGINPROPERTY (SL.name, 'PasswordLastSetTime') DESC

To change all databases to Simple Recovery except system databases

USE MASTER

go
declare
      @isql varchar(2000),
      @dbname varchar(64)
     
      declare c1 cursor for select name from master..sysdatabases where name not in ('master','model','msdb','tempdb')
      open c1
      fetch next from c1 into @dbname
      While @@fetch_status <> -1
            begin     
            select @isql = 'ALTER DATABASE @dbname SET RECOVERY simple'
            select @isql = replace(@isql,'@dbname',@dbname)
            print @isql
            exec(@isql)
           
            fetch next from c1 into @dbname
            end
      close c1
      deallocate c1