In most cases, you may have given an application only two pieces of information to connect to a SQL Server installation:
The network name of the server running SQL Server
Your login ID
Login IDs are the account identifiers that control access to any SQL Server system. SQL
Server will not complete a connection unless it has first verified that the login ID you
specified is valid.
When using Windows NT Authentication, you do not have to specify a login ID or password when you connect to SQL Server. Your access to SQL Server is controlled by your Windows NT account or group, which is authenticated when you log on to the Windows operating system on the client.
When connecting, the SQL Server client software requests a Windows trusted connection to SQL Server. Windows NT will not open a trusted connection unless the client has logged on successfully using a valid Windows NT account. The properties of a trusted connection include the Windows NT group and user accounts of the client that opened the connection.
So have a look at your SQL Server connection settings in the Server properties.