Yesterday while I was restoring my hard disk from a recent backup my CPU's temperature alarm went off. My CPU is a 3.2 GHz Intel Pentium 4 (Northwood). Listen to the alarm. The CPU also overheated a couple of days ago when I was running a link-checking program (CyberSpyder) for my Animal Pictures and More web site. Letting computer components get too hot shortens their lives. Dust reduces airflow and contributes to overheating. I decided I needed to clean my computer to make it run cooler.
I turned off the computer, vacuumed the top of the computer case and the surrounding table, and removed the cover. I vacuumed the front air filter, the rear fan grills, and the inside of the computer as best I could, gently, using my vacuum's furniture brush. I got an electric-shaver brush and brushed between all the fins of the CPU's heat sink. That was delicate work, fractionally turning the fan blades in order to reach all the fins. Then I brushed the fan blades on my rear case fan, especially the edges where there was accumulated dust. Finally, I brushed the heat-sink fins and fan blades on my video card. I made a cardboard cone and taped it to the end of my vacuum cleaner so that I had a small, non-conductive nozzle that sucked hard. I carefully vacuumed up the dust I had loosened with the electric-shaver brush. Then I put the cover back on, stood the computer upright, and turned on the power. The computer still worked. (grin)
I sometimes run a program called SpeedFan that shows temperatures from several sensors inside the computer. I think my CPU alarm goes off when SpeedFan says the CPU temperature is 147 degrees Fahrenheit (64 degrees Celsius). For weeks my CPU has been running between about 127 and 140 degrees F (53 to 60 degrees C). After cleaning, the CPU stayed between 96 and 100 degrees F (36 to 38 degrees C). That's a big improvement.