Hibernation issues

[prince1142003]

I have a wierd problem on my hands. My computer's set to hibernate after 2 hours of inactivity. Problem is, it never does. It resumes from a sleep cycle as if to hibernate, but stays powered on. If left on, it'll cycle through another sleep cycle, power on, and resume the process. However, when hibernated manually, the procedure works. But I would really like to be able to turn on auto hibernation.

Here's my system specs:
Asus M2R32-MVP
AMD Ahtlon64 X2 4600+
1GB RAM
PCI-e graphics
Windows XP Professional (32-bit)

And I've checked, all my drives have at least 2GB of free space, so space for hiberfile.sys shouldn't be an issue.

Any help is appreciated.