Hi
Try installing EasyBCD and see if it will make the boot menu appear.
It will configure the bootable OS's and show you the boot order etc, and there's a check box for show boot menu.
EasyBCD
Scroll down there's a free version at the bottom of the screen.
Link Removed
If the Android OS isn't shown when you open the window, then you click on Add New Entry and select and add it to the list.
You can select the default etc, through the Edit Boot Menu tab, I think this is where you will find the check box to show or not show the boot menu.
Mike