I've had to send my A75 in twice - once under warranty after 6 months, once after warranty was over. Each time they replaced the motherboard and fans, and I think some heat-sink paste. The second time they did it only as a "courtesy repair", but I believe it should also have been considered a warranty issue. At any rate, these apparently have an overheating problem that eventually leads to the machine suddently shutting off. No blue screen - just dead. The fans run nearly all the time on mine, and anything you can do to improve airflow through the PC will help, but Toshiba needs to step up and admit to a design flaw in this model. The P4 CPU must just generate more heat than it can move out of the case.
My A75-S209 has an overheating problem and will shut off after 5 to 20 min. depending if it is downloading. I've checked the underside and notice that only one fan is running. Are they both to run at the same time?