If Microsoft Office SharePoint Server (MOSS) and your database (MS SQL Server) are running together on same physical server, changing the name of the server (computer) using operating system may create non-functional SharePoint website.
When you change the physical server name the SharePoint is already connected to the SQL instance of old computer name (OldServerName/SQLInstance) and on changing the name the SharePoint will not able to connect the SQL Server as now the SQL Server instance will run on new computer name (NewServerName/SQLInstance).
To solve this problem you need to reconfigure the entire Microsoft Office SharePoint Server with SQL Server Instance. Please follow the steps to fix the issue.
1. Open command prompt, change directory to where stsadm.exe exists.
C:\cd C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN
2. To invoke setconfigdb operation we need to use stsadm.exe. Run following command on command prompt
stsadm.exe -o setconfigdb -databaseserver ServerName -farmuser MyUserName – farmpassword MyPassword
3. Go to IIS, All Programs>>Administrative Tools>>Internet Information Service (IIS) Manager.
4. Right Click SharePoint Central Administration v3, click on delete and re-run the configuration wizard; the web application will be re-created by the configuration wizard.
5. After the above operation has completed successfully, run the SharePoint Products and Technologies Configuration Wizard.
All Programs>>Microsoft Office Server >> SharePoint Product and Technologies Configuration Wizard
6. Complete all the steps of wizard by clicking on Next button.
At the end of this process you will get a success wizard.
On completion of this whole procedure Microsoft Office SharePoint Server gets connected to the database with new Computer Name.
Reference : Pinal Dave (http://blog.SQLAuthority.com)