http://www.makeuseof.com/tag/when-power-saving-fails-fixing-windows-7-hibernation-issues/
The short version:
- update all hardware drivers
- disable and re-enable hibernation to delete and recreate the hiberfile.sys
(run powercfg.exe /hibernate off and powercfg.exe /hibernate on) - in device manager, turn off all devices that are capable of waking the computer (particularly NICs)
- turn off the auto-hide task bar
- in power options -> advanced settings for the active power profile, disable hybrid sleep