Hibernation does not work, I’m always returned to the sign in screen
I've enabled hibernation in the power settings and the hibernate button is available in the start menu. But when I click on that the screen is fading out and it's going back to the login screen. It's not hibernating.
About my laptop:
OS - Windows 7 SP 1 Processor - Intel Core i7.
Last thing I did: Earlier when I got the system with pre-installed windows, it was working. But formatted the system and installed Fedora 17 and Windows 7. After that it's not working.