Thinkpad x220 cannot hibernate

[luthedang]

Hi everyone
I've just received thinkpad x220 few days ago, it's ID : 42872VU, with genuine windows7 proffesional. it's great but i find a problem later. when i want to put it in hibernation, it just turns the display off and require pw to log in again. I also search the solution from google but it's no use. So i think my x220 misses some necessary drivers. What should i do?

Ps : i'm vietnamese, i'm not good at English, please sympathise with me if my words cause you trouble to understand ^^