Hibernation just stopped working on my laptop a few years ago. I have tried to fix this at various times over the years with no luck. I know the problem has to do with my OS (not any acpi bios settings etc or firmware) b/c i've tried putting my harddrive in an identical laptop and that didn't help.
I've tried updating every power management related driver for my thinkpad x41. Apparently there is some bug in XP which gets screws up hibernation when you have more then 1 gig of RAM. I have 1.5gb. But, all the suggestions i found never helped this.
I have one additional symptom: I do not have a hibernate tab in power options.
I do have a c:\hiberfil.sys file consuming 1.49gb (I have 1.5gb of ram).