After fresh install of windows 8 on an old computer (7 years old P4 with ASUS motherboard) it freezes-up / hangs from time to time.
Using windows key + X you can open the event viewer and see when and what happened right before the freeze. For me there was always a “Some processor performance power management features have been disabled due to a known firmware problem. Check with the computer manufacturer for updated firmware.” message with “Kernel-Processor-Power” event ID 6.
Googled and still not sure what it is. Tried to change the power plan’s cooling system set to passive instead of active.