Never forget (opposite to my own experience) that your PC needs to be cleaned a little soemtimes. For me, the fan of my Athlon XP 2600+ CPU saw so much dust accumulated during the last months that the CPU temperature had progressively climbed from about 50°C up to more than 74°C.
A mere duster, a blower or a vacuum cleaner set to the minimal power will be sufficient to improve dramatically the situation. I immediately moved from the temperature alarm sound (going over 73°C) to a much more normal 52°C.
A good advice. A small prophylactic act to remember.