08-15-2009 07:09 AM
Was really bugged by the failure of my T400s to automatically hibernate (according to the power plan timeout settings). Sleep timeout worked perfectly, and manually initiated hibernate also worked fine. But the machine would stay in sleep mode and when the timeout elapsed for hibernation, it never wrote the hibernation file and remained in sleep mode.
After search Google, found a Microsoft description of things which would prevent automatic hibernation. High on the list was the setting of 'wakeup timer enable', along with the registry entries which configure it. I verified that these were set properly on my machine. Then I checked the BIOS for the hardware wakeup timer enable, and found it set to 'off'. I ignored the warning screen (about potential for unexpected hard disk activity/damage if machine was being transported-- I have an SSD). Changing it to 'on' solved my problem.