5.1. does not boot afte installation

[Hutterer Robert]

I installed e 5.1 version from mini.iso.
Everything workes fine, but afte exiting the installation procedure the
system does not boot. (I have to reset the machine)
Also the "reboot" command does not reboot.
the system goes down, but after teh messages:
 
done
uptime: ...
 
it stops, no reboot
 
Is there any idea what is the reason
 
Thanks
Robert