If i read you right, then you want to give the user the chance to enter a number of serial numbers, and then enter a new row in your DataGridView for each of these, with the same information from the text boxes for each row?
If so, it's pretty simple.
Assuming your serial numbers are specific, rather than a range, and your users eneter then in a text box, separated by a ',' character:
private void button1_Click(object sender, EventArgs e)
{
TextBox tbSerials, tbDescription, tbUnitPrice, tbCount, tbDate;
DataGridView myDataGridView = new DataGridView();
string[] serialNos = tbSerials.Text.Split(',');
foreach (string sn in serialNos)
{
if (!string.IsNullOrEmpty(sn))
{
myDataGridView.Rows.Add(sn, tbDescription, tbUnitPrice, tbCount, tbDate);
}
}
}