SQL Server - Substring in the query

" Select * from tblPA where SerialNo LIKE '(@txtSearchSerialNo)%'"  ;
I want the query to return values for all the matches typed in the txtbox named "txtSearchSerialNo" 
 If I replace 'X%' Instead of '(@txtSearchSerialNo)%'" I get few serch results.
I have the following code.

SqlConnection celPwrConnection = new SqlConnection("Data Source=localhost;Integrated Security=SSPI;Initial Catalog=CP");		
string Cmd = " Select * from tblPA where SerialNo LIKE '(@txtSearchSerialNo)%'"  ;
SqlCommand Cmd = new SqlCommand(Cmd ,celPwrConnection);
Cmd.Parameters.Add(new SqlParameter("@txtSearchSerialNo", SqlDbType.VarChar,50, "txtSearchSerialNo"));
Cmd.Parameters["@txtSearchSerialNo"].Value = txtSearchSerialNo.Text.ToString();
celPwrConnection.Open();		
SqlDataReader dr = Cmd.ExecuteReader();
DataGridSearch.Visible=true;
DataGridSearch.DataSource = dr;
DataGridSearch.DataBind();
celPwrConnection.Close();

Thanks.

Try removing the parenthesis, as follows:

string Cmd = " Select * from tblPA where SerialNo LIKE '@txtSearchSerialNo%'" ;

If that doesn't work, try this:

string Cmd = " Select * from tblPA where SerialNo LIKE @txtSearchSerialNo + '%'" ;

Tried this before "did not WORK"
string Cmd = " Select * from tblPA where SerialNo LIKE '@txtSearchSerialNo%'" ; 

This "WORKED"
string Cmd = " Select * from tblPA where SerialNo LIKE @txtSearchSerialNo + '%'" ; 
 
Thanks for your time and help.

select @txtSearchSerialNo = '%' + @txtSearchSerialNo + '%'

 select *
   from tableA where somecolumn like @txtSearchSerialNo