if (dgTest.Rows.Count <0)
{
int i=0;
foreach(DataGridItem dgItem in dgTest.Items)
				{
				if(((HtmlInputCheckBox) dg.FindControl("chkItem")).Checked==true) //chkItem is the ID of the Checkbox in Item Template
 					{	
						i = i + 1;
					}
				}

if (i<0)
{
  // atleast one row is selected}
else
{
   // no row is selected}
}
else
{
  // No rows to select
}