Hi when i connect the sql server 2005 it will display this kind of error.

An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1)

suddenly im getting this kind of error because previously it working well.
pls tell what is the solution?
how the problem is occured?

pls help me.

So the error is fairly clear in that its indicating that something is preventing you from actually making the connection. Could it be that there is a firewall in between you and the SQL instance. Or, as indicated in the error, the settings do not allow for remote connections.

Since you indicated that it was working before, either someone made a change to the configuration in SQL, or the traffic is not making it to your SQL server.

Have you lost connection to this server? can you PING it? Is this server hosted by your or a provider?