It's best to turn off Hibernation but you need an elevated Command form and you cant log in so you have to go about that in a different way.
If you don't have a Windows DVD you'll have to mash the power button as soon as the system starts up. Do that a few times and it will ged bored and should offer you the StartUp Repair options.
Choose to repair and the select Command Prompt. At the prompt, type
powercfg hibernate off
and hit the Enter key. Then type
exit
hit Enter again and choose the option to restart the system. Hopefully that worked.