The first step is deciding what amount of power you computer needs. If you have had problems and need to replace the old one, you should probably buy one that is a little more powerful. I say this because if the old power supply fried, it could be because it wasn’t big enough or powerful enough for the computer you are running. It could also be a faulty equipment problem not all power supplies are made equal. So if you are replacing a 400 W power supply you might want to buy a 450 W or higher. Keep in mind that if you are just using your computer for surfing the web you probably don’t need the most powerful one that you can find, just one that is slightly more powerful than the one you are replacing. However, if you are playing a lot of high graphic games on the computer then you may want to go with a larger power supply. It just depends on what the computer is being used for. Once you have the new power supply and are ready to install it, you need to turn off the power to