This blog shows you why the Query Designer is disable or grey out in Visual Studio.
When you get the View menu to open the Query Designer then you might realize all the buttons in Query Designer is grey out like the one below.
Go to the Data Connection. Right click on the connection then choose “Delete” to delete the database connection.
Right click on Data Connection then choose “Add Connection…”
Click on “Change… (button)” in Add Connection dialog.
Choose on “.NET Framework Data Provider for OLE DB (list item)”.
Click on “OK (button)” in “Change Data Source”
Select northwind database then click OK.
Expand the database till you can see the tables. Choose Products table then right click on “New Query (menu item)”.
You can see the Query Designer is working now.