freezing mac


I mainly run FCP but this problem can arise anytime with any application. But its seems to be occur more as more demands are placed on the machine.

My machine is a dual processor 2 GHz G5

During big FCP renders or when the machine is busy it freezes, if left long enough the fans then start to ramp up in speed and the only solution is a power cycle. During the freeze a small rede LED (light) comes on and is visible through the front mesh of the machine. So far I have read of other users having similar problems, blaming conflicts between the mac and its video card or a bug in the macs firmware controlling processor temp and cooling. Any ideas out there,... what does this red light indicate anyway... :(