You cannot put a computer that has more than 4 GB of memory into hibernation in Windows XP, in Windows Server 2003, in Windows Vista, or in Windows Server 2008

SYMPTOMS:

You can not put a computer running Windows XP, Windows Server 2003, Windows Vista or Windows Server 2008 in hibernation. Furthermore, the Hibernate tab in the properties of the Power Options dialog box is unavailable.

CAUSE:

This problem may happen because hibernation is disabled on computers that have more than 4 GB of RAM.

Hibernation wants enough disk space to have the contents of the computer's memory. Performance is reduced on a computer that has extra 4 GB of memory and that has support for hibernation. So, Microsoft has disabled support for hibernation on such PCs.

WORKAROUND:

Reduce the RAM to 4 GB or less on a PC that is running Windows XP, Windows Server 2003, Windows Vista, or Windows Server 2008, to solve this problem.

To solve this problem on a PC that is running Windows Vista, allow hibernation. To perform this, run the following command as an administrator:
powercfg /h on

To perform this, follow these steps:

1. Log on as an administrator.

2. Click Start, type cmd in the Start Search text box, right-click cmd.exe, click Run as administrator, and then click Continue.

3. At the command prompt, type powercfg –h on, and then press ENTER.

MORE INFORMATION:

To look the Power Options Properties dialog box, click Start, click Run, type powercfg.cpl, and then click OK.