The power supply, or PSU is a vital component to every computer and is often the most overlooked, until it malfunctions. How its possible to find if their PSU is malfunctioning, and not something else? One textbook sign of a failing PSU is frequent rebooting on its own. Another would be if the system doesn't start at all; that is to say, when you push the power button, there are no lights that start flashing and there is no noise of fans working. The third most common symptom that your PSU is going bad is if the fan on the back of it stops spinning.
So, how will we get this broken PSU out and the new one in? First unplug the PSU from the wall, then remove the side of the case. This is typically done with two bolts on the back side, however some custom case may have extra bolts or plastic clips holding the side in place. If you notice yourself exerting a lot of energy attempting to get this case apart, it is likely there is a plastic clip or an extra bolt which must first be removed.
Once the side of the case is open and the PSU is unplugged, remove all of the 4-pin power connectors from your devices. The power connectors attached to your devices will have 4 wires, two black, one red and one yellow. Next, remove the connectors from the motherboard . Lay the case on its side and, using a non-magnetic screwdriver, carefully remove the 4 bolts on the outside of the PSU attaching it to the case. If your PSU doesn't slide around with ease now, there may be an extra bolt holding the PSU to the inside of the case as well.
Here is where it will get tricky. On newer motherboards, you will have one large 24-pin connector, and possibly on pentium 4 and above, you may have one smaller 4-pin connector right next to the CPU. If your motherboard is older, and there is a power cord running from the power button to the PSU, you will have to almost definitely rely on EBay or a local computer show to get a new PSU. You will have to ask for an AT style PSU.
Watts will be printed on the outside of your PSU. You will want your new PSU's wattage equal to or greater than the old one. Gently place the new PSU in the case, with the AC adaptor facing the outside of the case, and the bundle of cords dangling inside. Again, using a non-magnetic screw driver, attach it with the same 4 bolts you removed from the last PSU.
