private void đăngNhậpToolStripMenuItem_Click(object sender, EventArgs e)
{
FrmDangNhap frmdn = new FrmDangNhap();
frmdn.Show();
}
private void Form1_Load(object sender, EventArgs e)
{
FrmDangNhap frmdn = new FrmDangNhap();
frmdn.ShowDialog();
}