Dell Optiplex 390 Reboot Issue in Linux

for debian squeeze amd64 on Dell latidute 390MT, with sandy bridge use reboot=pci

in details :

$>sudo nano /etc/default/grub change the : GRUB_CMDLINE_LINUX_DEFAULT="quiet" to : GRUB_CMDLINE_LINUX_DEFAULT="reboot=pci quiet"

(cltr+0, cltr+x)

$>sudo update-grub

reboot now works perfect