I’ve recently encountered an issue with systems having more than 4GB of system memory will not allow hibernate power option in both Windows XP and Windows Vista operated systems.
This issue usually occurs due to hibernation is being disabled on computers that have more than 4 GB of system memory.
Hibernation actually requires sufficient disk space to contain and accommodate the contents of the computer’s memory. Tendency is performance consequently is poor on a computer that has more than 4 GB of memory and that has support for hibernation. As a result, Microsoft has disabled support for hibernation on those kind of computers.
As a work-around on this issue, Microsoft suggests to decrease the system memory to 4 GB or less on a computer that is running Windows XP, Server 2003, Vista, or Server 2008. Not quite an option really but surely a leverage.