The problem may not be another installation, as the error suggests that the database can not be connected to, due to a server issue. This means that the forum may initialise without the correct configuration being loaded.
To fix the issue you need to findout why the database can not be connected to. It could be a configuration issue or it could be a corruption issue with the SQL Server or SQL Drivers.
Make sure that your forums SQL Server Database is set to auto start by editing the database properties. If you still then have the problem try reinstalling the SQL Server Drivers and if you still have the problem look at reinstalling the SQL Server.
You may need to also contact your host to get an expert to have a look at your servers configuration for SQL Server to see if they can find the issue.