Username & pwd verification ?

Question

Hi

Is there any way out to verify username and password using sql query to DB ..

Well actually i pre-requisite is i have say many columns i,e password and usernames ... so on 

I used query like this 

cmd = new SqlCommand("select username,password from studentform where username = " '+textbox1.text' and password= " '+textbox2.text ' " ,con); 

        con.Open();

        SqlDataReader dr = cmd.ExecuteReader();

        if (dr.Read())

        {

            Server.Transfer("studentafterlogin.aspx");

        }

        else

        {

            Response.Write("<script> alert('Invalid credentials')</script>");

        }

In above in my command , The select statement NOT WORKING PROPERLY i am not getting anything to datareader EVEN i given correct credentials ?? Problem in query ??

Help it please ....