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How to install a power supply
With all the cables unplugged and the retention screws removed, you can now pull the power supply free of the case. You may find it helpful to photograph which power cables went to which components so that you can have a reference for plugging in the cables on your new power supply. Power up the computer and test. Let it boot completely, then check to make sure there's power to the optical drive s and, if applicable, the front panel. The computer system should have available power and can be powered on.