The most important computer repair safety tip to remember is that before servicing anything on your computer, be sure that you have the power turned off. Even if you are only going to remove the computer case to look inside, be sure you have the power turned off. Many personal computers have internal lights, so be sure they are not on once you turn the power off. If any of the lights remain on, the power is not completely turned off.
Unplug your computer from the power strip or wall as a second safety precaution. Even though you may have turned the power to your computer off, there is always an outside chance that something remained on so unplugging the computer completely certainly solves that problem.