Hi
> I can not get the Startup menu to appear while holding both mouse button
If I remember right, you have to press the Escape-key [ESC] during startup to enter the early-boot menu of the Cyberstorm.
If you have a graphics card, you have to connect a monitor at the native Amiga video output for the early-boot menu. The AmigaOS early-boot menu is entered via pressing the left mouse-button during system start. If you use a PC-mouse and an adaptor like Topolino, this might fail, use an original Amiga-mouse for this purpose.
Noster