Searching A Databse

i'm making a web page for a clinic.
it needs to be able to search for patients by first name, surname, date of birth and patient number.
i'm using visual web developer and i have my database, my data source and GridView grid.
i want  4 text boxes for my first name, surname etc. when u click enter on any of them i want to retrieve all their data and display it in the gridview.
at the moment i have  one text box on the web page and through the "Configure data source" option on the grid view i can retrieve the specified data but for only this one item, e.g. SELECT * FROM [Patients] WHERE ([DOB] = @DOB).
 
if i add another text box to my web page, and don't do anything to it, the query wont run.
if i add and "AND" statement to the query, e.g. SELECT * FROM [Patients] WHERE (([DOB] = @DOB) AND ([FirstName] = @FirstName)), again it won'r run or return and data.
 
any ideas on what i can do or where i'm going wrong.
 
thanks