Windows 7 can sleep but cannot hibernate

In Windows 7, "Hibernate" is not on by default. You have to enable this option with the command line powercfg tool.

Here is a tutorial:

http://www.sevenforums.com/tutorials/819-hibernate-enable-disable.html

I noticed Microsoft has "Fixit" scripts which might automate this as well:

http://support.microsoft.com/kb/920730

I found out that one of the reasons why Windows 7 would not go hibernate was due to the hidden 100MB recovery volume has gone offline, for unknown reason.

In order to make hibernation work again, run DOS prompt as administrator then,

1. Issue the command diskpart and press enter
2. When the diskpart loads, issue the command select disk 0 and press enter, system should prompt Disk 0 is the selected disk.
3. Next, issue the command detail disk
4. System should now display a list of volumes on this disk. Look for the volume with 100MB size and note its number.
5. Issue the commmand select volume n where 'n' is the volume number you have noted (usually it is 0)
6. System should now prompt volume n is the selected volume.
7. Now issue the command Online volume
8. System should now prompt DiskPart successfully online the selected volume.
9. Issue the command detail volume, verify that the volume is now Offline : No
10. Finaly issue the command exit to leave diskpart, and issue command exit again to close the DOS prompt.

You should now be able to hibernate your system.

You may have to check your BIOS settings to allow for all sleep modes. The BIOS doesn't allow all power states sometimes, even if your Windows setting do. That's what I would recommend checking, as if you're seeing the Hibernate option in the Start Menu, then Windows must think that it's enabled.

Also, make sure that you don't have any programs running that would not allow the computer to change to a low power state. This unlikely has anything to do with your problem, but it's worth a shot.