SQL Server is terminating due to 'stop' request from Service Control Manager.

That is a normal shutdown message...same thing you would see if you went into the SCM (icon in the lower right corner and shut down the service manully, or from Control Panel.

When you have no message at all, its a SQL Server hang.

The sql server stopped around 9pm, and I found it and started on 10:40pm manually.

Usually what is the reason cause the SQL server to stop?

Also I set the server to 'Autostart SQL server', why it doesn't start automatically?

You should look at the event log on the server (application) to see if there were any events that caused the shutdown.

Also, just so you know, there is a technical area here on EE specifically for SQL Server that gets more traffic than this one does:
https://www.experts-exchange.com/Databases/Microsoft_SQL_Server/

Might get some additional responses since the bulk of your questions appear to be SQL Server related....

First, check all log files.  If you can see anything, this may be memory related.  Can you monitor your memory (with Performance monitor)?  

I've also seen recommendations to reserve more physical memory for SQL server as well as define a maximum limit for memory usage by SQL server (in Enterprise manager by right-clicking your server and choosing properties.)

I just asked my IT system manager, actually there was 'off-line system backup' scheduling at that time. That is why the SQL server stopped. Usually the SQL server would be down for 1:30 mintues.

But why it didn't restart automatically as usual?