C# .NET - Linq code is not working

var result = from GridViewRow msgRow in gvCurUser.Rows
             where ((CheckBox)msgRow.FindControl("chkSelect")).Checked=false
             select gvCurUser.Rows[msgRow.RowIndex];

I want Only checkbox unchecked count in Gridview

You are usgn linq in wrong way that's why it did not working
LINQ query should be work on collection not with girdview control filter like you are using .
You need to first get linq query with where clause to filter result collection than you bind that collection with gridview control 
something like this

string[] cities = { "London", "Amsterdam", "San Francisco", "Las Vegas",

              "Boston", "Raleigh", "Chicago", "Charlestown",

              "Helsinki", "Nice", "Dublin" };

    GridView1.DataSource = from city in cities

                 where city.Length > 4

                 orderby city

                 select city.ToUpper();

    GridView1.DataBind();

Hi,
here is some code that will represent each DataRow with the Customer Object.

static void Main(string[] args)    
  {       
     List<Customer> customers = new List<Customer>();         for(int i=1; i<=10; i++)    
    {          Customer customer = new Customer();          customer.FirstName = "FirstName " + i;          customer.LastName = "LastName " + i;          customers.Add(customer);  
      }      
         DataTable customerTable = new DataTable();  
      customerTable.Columns.Add(new DataColumn("FirstName"));  
      customerTable.Columns.Add(new DataColumn("LastName")); 
       foreach(Customer customer in customers)
        {         
       DataRow row = customerTable.NewRow();        
              row["FirstName"] = customer.FirstName;       
   row["LastName"] =  customer.LastName;                
     customerTable.Rows.Add(row);     
   }   
   }
second example even you cann do like this also.
string[] Customers = { "sales", "marketing", "Hr", "Finanace",

        "pharmacy", "absgsgs", "kdfjjhkj", "kjieuiu",

         };

    GridView1.DataSource = from customer in customers

         where customer.Length > 4

         orderby customer

         select customer.ToUpper();

    GridView1.DataBind();

hope it helps you.