I installed Debian Squeeze on a multi-boot PC where Ubuntu is the first and bootable distro.Are you chainloading GRUB2s or are you loading Debian directly from Ubuntu's own GRUB2 version?
I boot direclt from the Ubuntu's own GRUB2 version.
Using GRUB2, the options 'nosplash debug --verbose' are used, but Debian freezes silently. How to make boot verbose to see what happen ?
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The changes you have done should be enough.
However other options were also tried without any result.
In what stage is the system hanging at? What can you see in the screen? Can you at least reach the GRUB2 boot menu? I would try to load Debian from SuperGrub2Disk or any other LiveCD just to test if it hangs at the same point.
Yes, the GRUB2 menu is reached (in fact, it's used to boot the other system on same PC). The Debian system hangs direcly. Nothing is displayed. Yes, a LiveCD Debian 6 works fine (however it was a i386, the installed Debian is a amd64, the working Xubuntu is also a amd64).
Bye, Bruno