Why do computers fail?  This is a rather interesting question and one that deserves some investigation.  After all, if we know what makes a computer fail, presumably we increase the life of new computers.  The following discussion applies to common, generic office workstation. 

Generally speaking there are only a few moving parts in a computer to wear out, fans, CD–ROM drive and hard disk drive.  CD-ROM drives are only “in motion” for a relatively short amount of time in normal use.  We use them to load software, maybe backup files once in a while or play some music, but most of the time they sit idle.   Also, they are cheap and easy to replace.  A modern computer will have at least two fans, and probably more.  Failure of a fan is one of the leading causes of computer failure as it allows heat to build up on a component or in an area of the computer.  Your computer is made up of semi-conductors (integrated circuits, IC’s, “chips”) and these have a property that causes them to become more conductive as their temperature rises, causing more heat, and so on and so forth, thermal runaway.  Fans should be checked at regular intervals.

The dirty little industry secret.  Heat plays another role in shortening the life of a computer. This has to do with the electrolytic capacitors in the computer. Electrolytic capacitors have a finite life expectancy at a specific temperature and they are sold this way.  The temperature range is from 85-125 degrees C and the life is between 1000 and 20000 hrs.  So when you buy capacitors, you can specify, for instance, you want a 1800uF capacitor with a life expectancy of 10,000 hrs @ 105 degrees Celsius.  Computers don't run anywhere near these temperature and the life increases with cooler temperatures, but a capacitor with a longer life will outlive a shorter one at any given temperature.  As you probably have guessed, longer life, higher temperature capacitors cost more.

In the image on this page, three capacitors are shown in various stages of breakdown.  The one with the most leakage (left most) is closest to the CPU and therefore the one in the warmest location of the three.  This board is still functioning, but probably for only another six months or so.  When capacitors breakdown like this, the computer will exhibit any number of symptoms.  In the early stages, it may look like the PC is infected with a virus.  Latter it will be hard to boot, or freeze up, and finally, the machine will fail to power up.