SQL network error 26 win forms

I'm constantly getting this error when I try to add service based database to my new project (windows forms).

Same thing happens when I try to compile开发者_StackOverflow中文版 project which I have finished before (I haven't changed a single line of code)

The strangest thing of all is that I get same error when I try to run any of my programs using database.

Thx in advanced

IMG: http://i.stack.imgur.com/UjgHm.jpg

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This is because your connection string is wrong. One possibility is you specified one of the following parameters wrongly; server name, port number, username, password etc.

Also, this site rocks to check your syntax: http://www.connectionstrings.com/