Hi Vaughan,
The Hiberfil.sys hidden system file is located in the root folder of the drive where the operating system is installed. The Windows Kernel Power Manager reserves this file when you install Windows. The size of this file is approximately equal to how much random access memory (RAM) is installed on the computer.
The computer uses the Hiberfil.sys file to store a copy of the system memory on the hard disk when the hybrid sleep setting is turned on. If this file is not present, the computer cannot hibernate.
I would suggest you to delete the file in Safe mode and check. Ensure that the hibernation is not enabled.
If you still cannot delete it, use Windows 7 installation disk to boot the computer into safemode with command prompt and execute the command to delete the file.
For more information, refer to the link.
How to disable and re-enable hibernation on a computer that is running Windows
Please post back with the results and we will be happy to assist you further.