Unable to connect to database. Check database connection information and make sure the database server is running

In the morning, we were getting below production issue in all SharePoint Sites.

Problem: Users getting errors saying that "Unable to connect to database.  Check database connection information and make sure the database server is running"

The SharePoint Farm appeared to have a login issue with the Database Server. The following error was noticed on the Database Server Event Type: Error
Event Source: NETLOGON
Event Category: None
Event ID: 5719
Date: 10/27/2008
Time: 9:36:22 AM
User: N/A
Computer: SQL DB Server Name
Description:
This computer was not able to set up a secure session with a domain controller in domain AD due to the following:
There are currently no logon servers available to service the logon request.
This may lead to authentication problems. Make sure that this computer is connected to the network. If the problem persists, please contact your domain administrator.
ADDITIONAL INFO
If this computer is a domain controller for the specified domain, it sets up the secure session to the primary domain controller emulator in the specified domain. Otherwise, this computer sets up the secure session to any domain controller in the specified domain.

Resolution: one of my colleague just logged into our Database server with SharePoint service account to verify the account was not locked out.  He was able to log in without error.  Almost immediately after logging in, the Database Connectivity issues started to clear up and we were able to open all SharePoint site and central admin site without any the errors.

We didn’t figure out the exact root cause for the issue, because we already looked into SharePoint Log, event log  and database log, but at the last, we found that in some particular time of period there were problem with SharePoint AD service account, and by just logging into server, it gets resolve.

I’ll update you, if we find the root cause for the problem.