And you can't turn on Hibernate mode from Power Options Panel, it says: "The process cannot access the file because it is being used by another process".
I found one crasy method how to resolve this problem on my computer (AMD64/1G RAM/MB Asus M2NE/Video Asus N7600/IDE HDD).
- Delete file: WINDOWS\system32\drivers\atapi.sys (it will be restored by Windows).
- Manualy enable hibernate mode (now it isn't throw error message).
- Switch computer to Hibernate mode.
Is it helpful?