Help! Unable to boot from cdrom=ubuntu.iso

No window opens up so there’s no user output at all.
I tried to boot from an appvm and a standalone. Tried HVM, PVM, Nothing shows up.

Without knowing exactly what you tried it is impossible to say what’s
going wrong.
Open the settings for your standalone:
make sure you have adequate memory, uncheck “Include in memory
balancing”, set Kernel to “provided by qube”, and Mode to “HVM”.

Open a terminal in dom0, and run:
replacing STANDALONE with the name of your standalone,
QUBE with the name of the qube which holds the ISO image,
PATH_TO_ISO with the full path to the iso on QUBE.

Observe the output.
Report back.