Thanks, I watch your words and seems understand what ,where I was wrong. I try localhost\sql2012. It works.

My question Is :

My SQL server is SQL 2012. right now I can connect to remote server but connect to localhost is always failed. Can you tell me what reason...

And message include,cannot find default browser

I named my SQL server : SQL 2012. If cannot connect to it,it means cannot find SQL 2012. But why say cannot find default browser?

Error:2