Your question is your answer.
If the system tells you that there is no row at index 0, then it means you haven't returned any data from the database.
You can fix this by performing a quick check before your assignments.
DataTable dt= cc.searchbyname(txtsearch.Text);
if( dt.Rows.Any() )
{
DataRow row = dt.Rows[0];
sc.lblname.Text = row["Cust_Name"].ToString();
sc.lblphone.Text = row["Cust_Phone"].ToString();
sc.lbladdress.Text = row["Cust_Address"].ToString();
sc.lblemail.Text = row["Cust_Email"].ToString();
sc.lblcompany.Text = row["Cust_Company"].ToString();
sc.lblid.Text = row["Cust_Id"].ToString();
}