You will need
  • computer, power supply, small Phillips screwdriver, minimal skills in handling computer
All the described operations should be performed with the power off of the computer. Disconnect power from the system unit.
Open the side cover housing with side access to connectors on the motherboard. The unit of power most often located above the Board, but there are other options. Find it.
From unit supply to components inside your computer are the cables, disconnect them. Carefully remove the cables of the power supply of the hard drives and optical drives. If the cable power is connected to the graphics card, also disconnect it, squeeze the latch-lock.
Remove the primary and secondary cables to the power sockets of the motherboard. They are also equipped with latches that must be folded. Pull the cables carefully, you can gently sway them in the nest, but do not exert too much effort. Check that all the wires inside the computer coming from the unit power supplyhas been disconnected.
Remove the four screws that block the power supply bolted to the hull. They are located on the rear panel. While holding the second hand unit is power, so he fell inside the case for something important.
Gently, slowly then pull the power supply out of the chassis. You might have to remove the optical drive or the CPU, but in most modern cases this is not necessary.