Processors - How do I know if my computer is overheating?

Note

Intel® processors have built-in thermal protection. If the processor gets too hot this built-in protection will actually shut down the computer. If your computer is not over-clocked and is running under the design specification, this should prevent damage.

Unusual fan sounds. Most computers have two fans - one that cools the power supply and one that cools the processor. These are some of the first computer components to fail. The first indicator is a change in the sound it makes: if your fan starts to sound differently than you are used to (unusual whirring, clicking, clunking or groaning), it is time to have it looked at. On some models - especially those with "whisper quiet" fans – you will hear a musical sound or beep as a warning. If the fan is the problem, always replace, never repair.
Going "blue." If either fan does go out, the computer may boot up properly, but start to overheat shortly thereafter. The most common response is blue screen. If your computer gives you constant Windows* errors that turn the entire screen blue, check the cooling fan. Another indicator: lack of air coming or going from your case.
Constant rebooting or shut downs. To prevent damage to components, the computer shuts down or reboot if it senses an overheating issue. Sometimes the machine will do this every few minutes until the problem is fixed. This often happens if your computer's CPU is overclocked - sped up past its recommended speed limits. The BIOS will usually let you know if a thermal event has occured.
Non-fan-based CPU overheating. A CPU that overheats even if all fans are working (and assuming all cleaning, location and environmental temperature recommendations have been met) could need new thermal compound between its heat sink and processor. This eventually happens in all machines as the existing compound hardens, although it usually takes years. You can see a computer technician or buy a professional grade thermal compound and apply it yourself - but only if you know exactly what you are doing.