Why calendar is not show, but booking form is visible ?

Usually, this issue is relative to conflict(s) with some theme or plugins of the Booking Calendar version 3.0 or older. So please update firstly , your version of booking calendar to the most recent version. Otherwise try solution bellow:
This situation can be, when some other JS script (from some other plugin or active theme) is generate JavaScript error. You can check if you page have errors at the IE at the status bar or at Firefox using Console2 addon. So you need to fix that JavaScript error, or deactivate plugin or theme, which is generate that error. After this Booking Calendar will show up.