So the PC freezes, not just the audio...
Most likely a heat problem (as mentioned before), use a motherboard monitoring tool (
http://cdmediaworld.com/hardware/cdr...re_utils.shtml) to check the temps and to see whatever is wrong when it freezes
Maybe you are overclocking your PC, reset it to it's default setting and see if the problem is gone
On some Asus boards (e.g. the P4C800) up the memory voltage 0.1 or 0.2 volt. This helped me after searching for weeks why my P4C800 hang after a hour or so... I almost killed the board out of frustration over it...
If it is audio related then update to the latest audio hardware drivers! Usually the CD supplied drivers are buggy, especially if it is a new mainboard