sql query

Hi all, i have 2 textboxes one is FromDate and another is ToDate 
in sql server only one field of start_date to apply the fromdate and todate 
when i pass the date in query it does not come the data
Dim sql As String = "SELECT [request_id], [userID], convert(char(20),start_date,103) start_date,description FROM [M_Request] where start_date  >" & Convert.ToDateTime(txtDate.Text) & " AND start_date <" & Convert.ToDateTime(Me.txttoDate.Text) & "order by request_id desc "