Summer's here: Cool it down!

Most desktop PCs run comfortably when their internal temperature is between 16 and 43 degrees Celsius. Internal temperatures over 43 degrees can stress delicate circuits and electrical contacts, which may substantially shorten your computer's life. Hard drives are especially vulnerable when the temperature goes up: Data transfers slow down, and data written to the disk is more likely to be lost. Here's how to beat the PC heat:
Big amplitudes: The biggest temperature changes occur when you turn your system on and off, so leave your PC on but use its power-management functions to keep its innards as cool as possible when it's idle.
Fans:

The primary air mover in most PCs is the power-supply fan, although some systems have an additional ventilation fan built into the case. Even in relatively clean offices, dust can accumulate on the fan intakes and seriously obstruct airflow. Clean your PC's fans and fan intakes regularly, especially if you hear a change in the fans' one-note whir. If your CPU's fan or heat sink stops functioning properly, a CPU failure won't be far behind.
Monitor your temperatures: There are many programs which can show you the CPU and Chipset temperatures, as well as the fan speeds, but some of them don't support your hardware, so in most cases they won't show the correct values. The BIOS shows the most correct values, because it's built especially for your mainboard.