The Macs G5 had a problem that did end up in failures many times, though there might be a way to help it. There are register reset button on the mother board when reset can help. My G5 had its mother board zap out and since it was under warranty it was replaced, but since then I would get the curtain of death and if I don't shut it down soon it'll run the fan very fast until shut down. I tried the reset and it has only had a problem once in the past two months...seemed to help...Our art dept on campus had many problems like this with their G5's...they found that if the reset did not solve it then the mother boards did need replacing which costs a lot. They have not had the same problems with the new intel based machines...

In other words what you are experiencing is what others have experienced...

Astro typing on macbook pro...