I'm something of an expert myself

Load bearing dust

Often this is because of those little shit pin connectors for the power button getting pulled loose. How has a better, standardized option not been made for those yet?

Also remember to flip the switch on your power supply
- remember to plug the cord back into the power supply
Pretty much every motherboard in the last 10 years has shifted to the “Intel Standard” layout:
Most midrange to high end cases have a single connector that fits right on there, for compatibility they include a breakout adapter.
There's so many mobo connectors that clearly were not designed with cycle count in mind.
- USB 3 connectors, for starters. Unplugged mine for the third time to change motherboards and a couple pins just ripped out so now only one front USB works
The pinouts on motherboards actually has been mostly standardized, it’s just that case manufacturers can’t guarantee that your putting a motherboard in with that standard layout

"Oh, I forgot to turn the PSU back on"

I spent 20 years as an IT admin. We used cans of compressed air to clean dust out of computers. Light, gentle sprays, preferably cleaned outside so the dust doesn't just fill the room.

If you hold down the spray button for a few seconds, the can turns ice cold really fast, so be sparing with it. Also, don't tip it upside-down while spraying or it'll spray liquid that can damage computer components.

In all the years blowing dust out of computers, the only time I actually damaged a computer was when I tried to use a vacuum hose blowing air in reverse. It was too rough and broke some motherboard components.

I believe that vacuums also generate a ton of static charge as the air flows over the plastic hoses and such. They make special vacuums for electronic that are static free but expensive.
https://metrovac.com/collections/electronics-it/products/datavac-electric-duster
- Those things are amazing though, I've had one for over a decade now and it's the best 100 dollars I ever spent.
I work in a shop with compressed air for air guns and I use it on the insides of computers all the time to clean out the dust and haven't ever broken anything.
- If you’re using air compressors, you should consider adding a moisture filter on your air gun. When the air gets compressed, it gets hot. And hot air can hold more moisture. Then when you spray it, that air cools back down and the moisture re-condenses as it leaves the system. You can very easily fuck up electronics because you blew a bunch of water mist into the connections at 60 PSI.
  It’s also why (unless you’re using a compressor specifically designed for it) you should be opening the dump valve and draining it entirely after you’re done using it. Don’t just let it sit with compressed air in the tank for weeks at a time. All of that humidity will slowly condense as the air in the tank cools, and you’ll end up with liquid water inside of your tank. And that’s how rust happens. If you never empty your compressor, you’re not only spraying rusty water everywhere; You’re working with a time bomb. It may explode in a year, or five years, or fifty… But that rust will slowly eat away at the internals, and weaken components that are designed to hold a LOT of pressure.
  Source: I live in a humid area and occasionally use air compressors to clean electronics.

Yours isn’t dishwasher safe?

Forgot to add the detergent

Never touch a running system

Check if maybe any dust got into the connectors. Prone to thus is the PCIE connector on the motherboard, when removing the GPU. Just blow into it to make sure its dust free. Happened to me more than once.

My fear every time

Never actually happened, but still

Is it connected?

Happened to me once, my wife won't let me forget it

Yea 409 isn’t the best for the longevity of a PC.

it reminds me of that Macbook vs thinkpad meme.