I have a log in form, in Form_Load disable the explorer.exe to disable the alt + tab keys so that the focus is on my log in form that is fullscreen. when i logged in my log in form my application will show and my login form's hide.

LoginForm.Hide()
Application.Show()

Vice Versa When I close my Application Form

Application.Close()
Login.Show()

My Problem is the Form_Load is not loading, it should disable the explorer.exe again.When my Login Form Show. Any codes that enable my Form_Load again when i close the application.

It seems to me like you closed the form before calling Login.Show(). Try:

Login.Show()
Login.SetFocus()
Application.Close() '[or Application.Hide()]