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My screen sometimes becomes annoying. Gray horizontal lines occur on my screen. I've changed my Graphics Card. But nothing happened. I changed the monitor power cable and 80% of the lines disappeared :) but there's still some.

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Have you tried replacing the video cable between the monitor and the computer? – Justin Pearce Feb 17 '12 at 21:39
Yeah. Actually, I connected the monitor to different power outlet and the problem is gone. But I can't figure it out why it's noisy when I connect the two cables on the same power outlet! – 0xab3d Feb 17 '12 at 22:36
If you figured out what the problem is, can you please post a self-answer below explaining what you did? In 2 days, if there isn't a better answer by then, you can accept your own answer, indicating that the problem has been solved. – nhinkle Feb 18 '12 at 0:36
It sounds like you might have power going to a case that should not, or improper grounding. I have only read about 2 people who discovered that a ac wire was touching their case from the computer PSU. (poor Psu QC) something Like that (but mabey not that) could exist. there are ways to test for some of these thing. A simple tiny neon bulb , a voltmeter, checking the house wiring itself with simple polarity/ground testers. Are there any items around there that would cause normal interferacnes? You covered nothing in the question, we dont even know the connection style? – Psycogeek Feb 18 '12 at 2:41
Thanks Psycogeek. I don't have any testing equipments here. I will buy a voltmeter but How should I use it? Connect one terminal to the ground and the other one to the case? And what readings should I have? – 0xab3d Feb 18 '12 at 9:11
up vote 0 down vote accepted

It's been like more than one problem :) I eliminated the ground wire and 90% of problem was solved, then I changed the VGA cable and I got it. It's wavy-lines-free :)

Thanks guys

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"Eliminated the ground wire"? What, exactly, does that mean? If it's what it sounds like to me, it sounds like you have a bad ground in your electrical box, and it needs to be fixed pronto. (I once had a ground lead in an outlet that was giving me ~50 volts. Baaaad news.) – Heptite Mar 2 '12 at 20:22

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