my connection string

Data Source = .\\SQLEXPRESS; AttachDbFileName= path\\datbasename.mdf;Connect Timeout=1000;Trusted_Connection=True

Is the SQL Server using mixed mode, or Windows authentication?

Windows authentication

Is the SQL Service running?

yes

What are you attempting to do when you get the error?

i have used the SQL server...

default database is master

I have default login of the windows mode (local system account)

I have default login of the windows mode (local system account)