I have been experiencing some strange behaviour on my computer. It happens at times when the kitchen light switch is turned off although my computer is in the study room. If I am surfing the web, the browser would automatically resize. If I am writing on a word processor or text editor, some random characters would appear. How do I protect my computer from such random occurrence?

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    You have a poltergeist, there's not much you can do apart from try to get him onside and ask him to stop messing with your stuff. – Dan Jun 6 '12 at 9:42
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    Do you have a wireless keyboard perchance? – Chris McKeown Jun 6 '12 at 9:44
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    just curious, what kind of monitor? what kind of keyboard? This is a really cool question but we need more details. I'd wonder if a microphone in the area would pick up anything – Journeyman Geek Jun 6 '12 at 9:50
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    @dan Time to call in a priest I think. :) – Rippo Jun 6 '12 at 10:02
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    Curious whether you ever solved this. Is the computer on a UPS (often provides some level of power line filtering)? I have an old Palm PDA that I still use. It recharges in a USB cradle (power only, no signal connection), that is plugged into the same wall outlet as a fluorescent desk lamp. I shut off the PDA while it is recharging. If I switch off the desk light, the PDA turns on. Bluetooth is its only wireless interface and that is powered off, so the phenomenon is through the power line. It sounds like what you might be experiencing. – fixer1234 Apr 29 '15 at 0:59

It sounds like some kind of Electromagnetic Interference to me. If the issue is fairly reproducible (I.e., you can turn off the light and you know something will happen with 10 minutes) then I'd try and narrow it down by disconnecting your keyboard and mouse.

Additionally, if you're using PS/2 keyboard or mouse then swap them to USB and see if that helps.

You could also try to tidy up any cabling, disconnect any peripheral devices (Printers etc) and speakers, to see if that makes a difference.

Finally, it could be an Earth / Grounding issue. You don't say where you are, so without knowing your local requirements I can't say much more on this but I've seen grounding issues produce some very peculiar issues on computer equipment.

I can't fathom why the light being off would make a difference, but then it's hard to say without knowing what your wiring is like.

  • I can confirm it is the light switch as it happens on the instant when the light switch is turned off. I don't have an idea about the earthing system in my house except that it uses 230V and has live, neutral and earth wires. I remember once while repairing the power socket that the main circuit tripped despite opening the circuit breaker for that particular point. So you may be right about the earthing issue. Would like to read more about it if you have some materials. Thanks. – Question Overflow Jun 6 '12 at 10:21

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