Come controllo di non inserire dati duplicati???

Sto facendo così ma ci sono un paio di errori....
codice:
		public static void insertRecord (string tableName, string nome, string TxtbStato)
		{
 
			OleDbConnection conn = new OleDbConnection(connString);
			conn.Open();
			OleDbCommand comm = new OleDbCommand("SELECT * FROM " + tableName +" WHERE " + nome +"=" + TxtbStato ,conn);
			DataTable MyTable = new DataTable();
			DA.Fill(MyTable);
			if (MyTable=="")
			{
				OleDbCommand comm = new OleDbCommand("insert into " + tableName + " ( " + nome + ") values ('" + TxtbStato + "')",conn);
				comm.ExecuteNonQuery();
				conn.Close(); 
			}
			else
			{
				Response.Write("dato già presente");
			}
		}
1- c:\inetpub\wwwroot\ppp\areariservata\Access.cs(39) : The type or namespace name 'DA' could not be found (are you missing a using directive or an assembly reference?)

2- c:\inetpub\wwwroot\ppp\areariservata\Access.cs(40) : Operator '==' cannot be applied to operands of type 'System.Data.DataTable' and 'string'

3- c:\inetpub\wwwroot\ppp\areariservata\Access.cs(42) : A local variable named 'comm' cannot be declared in this scope because it would give a different meaning to 'comm', which is already used in a 'parent or current' scope to denote something else

4- c:\inetpub\wwwroot\bacchi\areariservata\Access.cs( 48): The type or namespace name 'Response' could not be found (are you missing a using directive or an assembly reference?)