There are issues with some Intel video cards xserver-xorg-video-intel and KMS and the default 2.6.32 kernel in Debian squeeze.
On my Intel-equipped Asus netbook booting from GRUB or starting an X session can result in a black screen and completely unresponsive system. A temporary fix is to edit the booting GRUB entry and add acpi=off to the kernel line.
A more permanent fix is to configure the backlight by editing GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=Linux acpi_backlight=vendor"
Update the grub configuration by running sudo update-grub2 and reboot.
Increase the brightness setting to maximum visibility. For example ... on my netbook I run:
$ sudo echo 15 > /sys/class/backlight/eeepc/brightness