Newbie fails booting: "Xen is relinquishing VGA console"

[Bernd Bausch <berndbausch@xxxxxxxxx>]

I am following the instructions at 
https://wiki.xenproject.org/wiki/Xen_Project_Beginners_Guide, except 
that I am installing the latest Debian. The machine is a Lenovo Thinkpad 
E540 with ample memory (16GB).
Trying to boot the Xen kernel, all I get is a dark screen. When I remove 
the "quiet" option from Grub's menu point, I see that the last message 
before blanking the screen is "Xen is relinquishing VGA console".
There are various documents on the internet that contain this string, 
but I am a total newcomer to the world of Xen and don't understand them. 
It might have something to do with "booting into domU versus dom0". I 
don't have a domU defined at this point.
I can boot into "normal" Debian without Xen.

How can I proceed? Should I use a different document to bootstrap myself 
into Xen?
Thanks in advance.