Be nice to your computer and maybe you'll be spared..
1 Electrocution
They say it's the amps that kill you, but it's more like the amp - or at least part of one: between 0.1 and 0.2 amps is enough to send you to the next life. Bearing that in mind, you'd think that sticking your hands into your PC case while it's turned on would be a recipe for instant death, but worry not. There's not enough voltage running across your motherboard or the components to overcome the natural resistance of your skin (if it's unbroken, anyway).
Your power supply, however, is another matter entirely, for within there be dragons. And when we say dragons, we mean enough electricity to grant you an express ticket to the great system builders' convention in the sky. So please, never open a power supply. It's simply not worth it.
2 Fire
Place your hand in front of an outgoing PC fan, and if the system has been on for a while, it'll feel warm. That, as we all know, is because electronic parts radiate excess heat. It's the reason we need heatsinks and fans, and it's also the reason your computer should be given a bit of space to breath. Blocking up the ventilation areas will cause overheating, and that, combined with potential electrical failures (especially from cheap, unbranded power supplies), means your PC could easily become an impromptu fireplace. Thankfully, a few safety measures, like getting a decent PSU, sufficient cooling and working smoke alarms should keep you safe.
3 Inactivity
In 2012, an 18-year-old man in Taiwan was found dead in an internet cafe, after spending around 40 consecutive hours playing Diablo 3. Clearly, he hadn't heard about the other Taiwanese chap who died in similar circumstances just months before, who reached a permanent game over state after just 23 hours. These are merely two of several such cases of extreme gaming sessions killing people, but it's not just gamers who are affected, and death can creep up more subtly. If you spend all day on the web or working at a PC, all the while eating doughnuts and crisps, you're probably fully aware that you're pushing yourself ever closer to an early grave.
4 The Are Other People Out There
Human beings are resilient creatures. You can take almost anything away from a man, and he can still bounce back. But never, ever take another man's virtual sword - especially if it belongs to Zhu Caoyuan, the Chinese who stabbed fellow gamer Qiu Chengwei for stealing and then selling his digital blade. The sword, won in the online game Legend of Mir 3, fetched 7,200 yuan (around £473 at the time), but it was Qui who ultimately paid the highest price. After failing to get the police to take action, Zhu tracked Qui down and stabbed him to death (with a real, rather than virtual knife). There were similar incidents in Nottingham in 2009 and in France in 2010. The fact is the internet makes it easy to connect with people in no time at all, and sadly not always in the most productive or healthy ways.
5 Self Awareness
Turn on your PC, and the processor instantly gets to work, making hundreds, if not thousands of decisions in mere seconds. Humans, by comparison, can spend an age trying to decide whether they want ketchup or daddy sauce on their chips (the potato kind - it's probably not good for CPUs). But in spite of these vast computational skills, artificial intelligence still lags significantly behind our own squidgy grey matter - for now, at least. When the robot revolution does happen, though, it'll probably start with small things, like search engines that guess what you want to search for before you've searched for it and voice controlled digital assistants that can make phone calls for you... Oh, hold on a sec, we already have those...