Repairing your own computer can be great fun, and can save you loads of time and money. But no amount of money saved is worth compromising your safety. Thus, some precautions are in order.
While the focus of this tutorial is on the hardware inside the case, it is worth mentioning that you should never, ever attempt to service a cathode ray tube (CRT)-based monitor (as opposed to the newer flat-panel LCD displays).
A charged cathode ray tube stores a lethal voltage that can electrocute you. Moreover, the vacuum tube itself can implode if broken or punctured, posing another level of risk to you.
There is also a device inside the case that you should not disassemble for servicing purposes: the power supply. The power supply is mounted in the inside corner of the case, and can be easily identified by the bundles of colored wires that are protruding from it. The power supply houses components that also store electrical charges. While it’s perfectly safe for you to work inside the case in the vicinity of the power supply, you should not attempt to repair it. The power supply should be regarded as a ‘black box’; when it fails, replace it.
In terms of your own safety, you should also make sure to turn the power off on the computer and unplug the unit from the electrical outlet.
There are other safety issues that have less to do with your own safety, and more to do with how you may inadvertently harm some of the components inside your computer. Certain components are highly susceptible to damage caused by electrostatic discharge (ESD), more commonly known as static electricity. While it takes about 3000 volts of static electricity for you to feel the discharge, certain electronic components can be damaged with as few as 30 volts of static discharge.