SQL Server does not exist or access is denied

The problem occurred on May 1. When I was sleeping late on vacation, I suddenly received a call from the customer saying that the webpage could not be opened.
This is the case. In the early May Day, I completed a customer's analysis system and used. NET + SQL Server to test it in the company. So I think everything is safe. In April 30, the system was loaded into the customer's notebook for delivery. As a result, the above problem occurs on May 1. I did not find the cause of the problem through telephone communication, so I suggest you connect him to the network for a try. The customer can use it after connecting to a hub.
I got my laptop back today and finally found the cause of the problem. I didn't patch SQL2000 with SP3 (I heard that SP4 won't work). After hitting SP3, the network was disconnected.
Write down this question. Maybe someone will have the same problem with me !!!