RESOLVED~
The problem somehow resolved itself after I reinstalled the game the fourth time.
I never experienced this problem in any game except Spiral Knights, so it's not the fan. The fan is normal 24/7, until the problem occurs.
I really have no idea what was causing this. It makes no sense.
ORIGINAL POST:
So, I've had this problem with Spiral Knights before, but it was never to this extent.
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I used to have this problem where, on rare occasions, my computer would spontaneously die for no reason, as if it had been unplugged. Upon turning it back on, the fans inside would start going crazy fast and it made a very loud noise, but nothing ever happened. Whenever I pressed the power button again, it instantly shut off like it had done just moments before.
I then had to let it stay turned off for about thirty minutes, or else I would not be able to boot the computer. The same thing would happen if I tried to start it too soon; after it reaches the "Loading Windows" screen, it would stay there for about two minutes, then the screen would go black and my monitor's light would go from white to orange, as if the computer wasn't on at all. The fan would start acting up again, and pressing the power button would make it instantly turn off.
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It was very annoying when that happened, but it was uncommon enough that I didn't really think much of it. At least until yesterday...
Within just five minutes of starting up Spiral Knights, that problem occurred. So after waiting for a bit and starting my computer back up, I tried to get into the game again, but I was faced with the same problem, only minutes after starting Spiral Knights.
Something I should probably mention is that the problem became how bad it is right now, right after I made an alt-account and downloaded the non-Steam client from this website.
I am literally unable to play the game now. This is such a bizarre problem, that I doubt anyone can help me, but hopefully someone out there knows how to fix this!
(Yes, I shamelessly left a shadow copy in General Discussion. Most people ignore the Technical Issues sub-forum)
My first thoughts are that your CPU could be overheating. Make sure that the CPU fan is working and doesn't have a bunch of dust in it. If that doesn't help, perhaps download some diagnostic software that displays the CPU temperature, and check the temperature when you are playing Spiral Knights.