[citation][nom]jamie_1318[/nom]CPU thermal sensor is irrelevant in a PSU failure. For the CPU to get hot enough to shut down a fire would have already started and become self-sufficient down in the power supply. same is more or less true for the mobo thermal sensor(assuming they have one).[/citation]
Not really, no. The motherboard chipset has lower thermal tolerance than the CPU. When the CPU gets hot, a lot of heat will dissipate from the heatsink, but the dissipated heat will reflect onto the chipset (Northbridge or single-chip, due to required proximity to the CPU), which itself generates less heat (so it needs lesser cooling - sometimes only passive) but also can't tolerate heat in response, and thus will alarm the motherboard thermal sensor often well before the CPU overheats, causing a system shutdown.
Best advice with every computer is have it checked out by a trained technician to disassemble and have your fans and heatsinks cleared from dust, lint, pet hair, smokers tar, etc., before it gums up your fans and blocks heatsinks. If your fan bearings are already rattling, it's likely already too late, so you'll need to replace those fans. Have it checked AT LEAST once a year, although some people need to have it checked once a month if they live in filth. If you can do it yourself, be my guest, but don't procrastinate. It's required maintenance and needs to be done.
Oh and CHANGE YOUR DAMN FURNACE FILTER! I see too many people that have pet hair and dust hanging out their filter insert because they don't change it regularly, and that's just gross! You should check it at least once a month. And make sure you put it in the right way around. If you have the cheap Walmart filters, replace them every other month. This is just general health advice, but cheap filters let lots of dust through, and it's bad for your computer, as well as your lungs. If you use central A/C, don't forget that it still works through your furnace vents, so it's still blowing dust through. Having your vents cleaned by a professional cleaning service once in a while doesn't hurt either.