The reason is when you set row filter on this line
dv.RowFilter = "job_id='" + s1 + "'";
dv doesnt contains any matching rows hence its empty. i.e dv has zero rows.
following this filter you are trying to access a zero index value. check the dv.Length or Count ( i am not sure about what data type dv is)
if( dv.Count > 0)
{
txtid.Text = dv[0]["visit_id"].ToString();
txtdate.Text = dv[0]["date"].ToString();
drpradio.SelectedValue = dv[0]["radiologist"].ToString();
drpstudy.SelectedValue = dv[0]["study_type"].ToString();
drpaccount.SelectedValue = dv[0]["account"].ToString();
radiobtn.SelectedValue = dv[0]["upload"].ToString();
txtaudio.Text = dv[0]["time_duration"].ToString();
txtremarks.Text = dv[0]["remark"].ToString();
Label4.Text = dv[0]["uname"].ToString();
}