System doesn't reboot properly

Hi,

most of the time when I do a reboot the sytems shuts down properly. But just 
before one expects to see the Bios information screen again (the one where 
devices are listed, Ram, Bios Version etc) the screen suddenly turns on the 
backlight angain with no content (it is black) and that's it. I always have 
to press the power button for a few seconds to switch it off completely. I 
have experiend this behaviour from the beginning of 5.x up to 6.

Jochen