I also have this problem. When i click, 'host' game it immediatly disconnects me from vent and from other net services, however it comes back after a second and people start joining my game. This didn't happen until the most recent patch.
No, "regular" software can't. It can cause an error and, depending on your Windows settings, this can cause your computer to reboot. (Yeah, Windows is software too, therefore "regular software".)Software can absolutely cause a restart due to a crash, it's actually pretty easy to cause.
If I'm allowed to speak: "one time my entire computer crashed. it just turned off completely, restarting itself" sounds like your PC overheated. A game usually can't restart anything, especially without asking. Your motherboard, however, might reboot if i.e. your CPU gets to hot.
But Magicka shouldn't turn your computer into an oven, especially if it "eats [others] for breakfast". Your fans of coolness +2 should keep everything at a nice level, no matter whether Magicka is causing an endless loop and using 100% of your CPU or not.
I can imagine that Magicka caused your computer to use 100% and your fans failed. Or one of your fans. Anyway, at least a mistake on both sides.
The only other possibility I can think of ad hoc is that your PC didn't restart by itself.
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