I recently had to replace the power switch in my PC's case and thought it might be helpful to share.

Truth be told this "build" is very simple and 7 pages is definitely overkill for installing a simple switch in a computer case. The actual motivation for writing this is to help diagnose bad case switches because misdiagnosis is easy, can waste a lot of time, and might cost a lot of money too. The fact that it rarely gets brought up as a potential problem, due to the aforementioned misdiagnosis, makes it even harder to remedy.

That said if you're just looking to upgrade, change, or otherwise modify your case this will still be helpful, if not a little full of faff.

Step 1: Diagnosing a Bad Switch

So how do you know you might have a bad switch? Your big indicator is random hard crashes, typically at boot, straight to power off. No blue screen of death or lock-up. Just on one moment, off the next. The reason that the case switch might go unchecked in a situation like this is two-fold. 1) Hard crashes like that tend to be the first symptoms of a dying power supply (PSU) or an overheating CPU and 2) who really suspects the innocent little power switch? I know I didn't.

Specifically my symptoms were: crashing at random points mid boot, sometimes mid-POST, sometimes while windows loaded, and occasionally on the desktop but still while it was pulling itself together, and not just once but several times in a row. I did have two crashes after it was running for awhile but these only served to obfuscate the real cause. I RMA'd my PSU ( sorry Thermaltake :/ ) and when the new one didn't solve it I pulled the CPU, cleaned the dust out of everything, and re-installed said CPU. It only ended up costing me $8 in shipping and 10 days of down time but if my PSU hadn't been under warranty or I had damaged something while tearing it apart it could have been a few hundred dollars to still not solve the problem.

The best way to test for a faulty case switch is to pull the case wires from the motherboard and then short the two pins that had previously led to the power switch. Personally I used the metal handle of a pair of nail clippers that were close at hand to test boot my system. That is a sentence I would never even have conceived of writing before this whole debacle, but here we are. If the switch is bad, booting this way should result in a clean launch, no crashing. If it still crashes then the switch is probably fine and you'll have to keep troubleshooting.

TLDR; if your getting random, repeated crashes on boot, break out the fingernail clippers and test your power switch pins.

Step 2: Materials & Tools

Materials

Momentary SPST (Single Pole, Single Throw) Switch - Your most basic momentary switch, press/flip/turn it to close the circuit, release and it opens.
2 Pin Wire Harness - I found one with long leads but the easiest way to get one that you know will work is to just harvest the one from your current switch. (99% chance the problem is in the switch, not the wires.)
Extra Wire - Only necessary if your harness doesn't have enough lead as-is. Match your gauge as best as possible.
Panel Nut - A thin hex nut that works with the washer to hold the switch to the case. Threads must match the switch body.
Washer - Backs the panel against the nut to hold the switch in place.
Totally Cool Switch Cover (Optional) - Might actually be helpful if you happen to have inquisitive young children, otherwise...

Tools

Step Drill Bit - The best bit for drilling round holes in thin materials.
Soldering Equipment, probably - How you make your wires stick good is your own business. Solder, tape, connectors, you do you.
Pliers - For tightening the panel nut. Small fingers will do as well.

Step 3: Switch Wiring

[Before you do any work on the computer, switch the PSU off or unplug it if there is no switch!]

My inability to throw away anything that might be even remotely useful finally payed off so assembling the switch "circuit" was super simple for me. Just a matter of plugging two wires in. At most though you'll be soldering a couple of connections, likely just two between the switch terminals and the wiring harness leads, especially if you harvested the wires from your current switch.

Of course this assumes your motherboards case switch works the same way as mine: essentially shorting two header pins with the switch. If that's not the case I'm not sure how you made it this far into the guide but you'll have to find your own way from here. i.e. Google Search is your friend.

Step 4: Case Modification

Start by measuring the size of the threads, or whatever part needs to stick through the case, on your switch. Using the step drill put a hole in the desired location that's slightly larger than you just measured but smaller than your backing washer or switch body.

One major note here: electronics HATE metal chips. A couple ways to prevent shorting something expensive are catching the chips,I just held a tissue under the hole with one hand (watch out for the bit coming through!), and putting tape over both sides of the drilling location. The tape is a little risky but frees up both hands so consider other methods, like holding a running vacuum cleaner hose to the hole while drilling.

Step 5: Install...

With the hole finished, put the washer on the switch, the switch through the hole, and tighten the nut on the threads. Finally plug the wires into the correct motherboard pins (it shouldn't matter which switch lead goes to which power pin).

Step 6: And Boot!

Remember to turn on or plug in your PSU before you try to boot. I've had many a heart-sinking moment pressing the power switch and getting nothing only to realize the PSU was still off. Avoid the stress if you can.

With everything juiced hit the new switch and hopefully you'll get a clean, crash free boot. If not, it's back to diagnosing for you. Sorry. If shorting the pins caused a boot, and still does, then the issue is probably in your modded switch so start there.

Hopefully this was helpful or at least not a total waste of time. As always, comments, questions, and pictures of your new switches are all highly encouraged!