SQL Server connection

I have SQL Server 2008 R2 on Windows XP. And I can't connect to SQL Server via开发者_如何转开发 Management Studio or ASP.NET. I try to connect to another SQL Server on a different server, I didn't connect either. My computer allows remote connections. Also there is no such a problem before and I had connected successfully before.

Error is:

Cannot connect to mycomputername.

ADDITIONAL INFORMATION:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (Microsoft SQL Server, Error: -1)

What should I do about this? Thanks..

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It sounds like it can't find the database instance you're trying to connect to. Check the PC on which the SQL server is running has the SQL Server Browser service running - that's needed for remote connections. Also check the firewalls at both sides are allowing UDP port 1434 (used for automatic discovery of SQL server instances) and TCP port 1433 (used to actually connect to an instance).

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Can you remote onto the box where the instance of SQL server is being hosted? Your error message is telling you that your connection string is pointing to an unreachable instance of SQL server... What's your connection string?