Hibernating/Sleep Problems

Hi there

When I try to put my computer to sleep, it goes ahead and sleeps, but I can
never wake it back up again. I'm on a home-built PC with specs as listed
below. I've tried moving the mouse/typing on the keyboard (both wireless),
pressing the power button, but it doesn't work. Every time I try doing that,
I end up having to manually power off and power on again, in which case
Windows knows and tells me Vista didn't shut down properly, what would you
like to do (the F8 menu).

So I tried hibernating. Worked for a couple times, then now, it will
promptly restart itself after "hibernating", sorta like a hybrid
hibernate-restart function. Everything restores back as if the computer had
finished hibernating, so no bad F8 boot menus or safe mode things.

Any suggestions? Thanks!

PC Specs:
- Asus P5K (no wireless)
- 2GB RAM
- nVidia GeForce 8800GTS
- Intel Core 2 Duo 2.4GHz
- Windows Vista Business - Activated
- Lian-Li P20-B Silent case (with power/reset LED/buttons PROPERLY connected)