Bizarre Horizontal Pixel Lines Through Screen (Application Windows and Desktop).

If the problem has persisted through an OS install, it's probably not a software issue. How are you connecting to your monitor? DVI or VGA? What is the run distance? Going by the image it looks like a bad DVI connection. This could mean either the run distance is too long (i.e. over the 15m recommended distance for DVI-D) and the signal is degrading, or the cable doesn't have enough shielding and it's picking up interference along the way. I would try reseating the connections (back of computer and back of monitor) and see if that helps. If it doesn't, try a shorter cable. If that works, you need a new cable, one with more shielding to protect the signal for your run distance. Monoprice makes great, beefy DVI-D cables for long runs. Cheaper than everyone else too. Good luck!

 

try a different monitor... try a dvi to vga adapter with a vga monitor.

if that doesn't fix it... move on to the video card.

 

There are some very long threads about this ATI card problem over at the Apple user forums. The typical solution is to get your video card replaced by Apple, apparently these artifacts are the result of overheating of some of the earlier revisions of the ATI cards. (That's the general consensus, anyway.)

 

I'm having this exact same problem with an NVIDIA card, and I just got my iMac back they replaced the video card, logic board, display...and that's the second time they've had to do it, help?

 

Doesn't matter. The windows could be corrupt in VRAM, meaning the corruption would scale and move with them.

Edit: %$%$% fooled by a dead thread.

 

I'm still here and need help, I just can't find very many references to this issue.

 

Your graphics card is dead.

 

+1. I've seen those lines too. When they persist and all the drugs have worn off, what they mean is: your graphics card is dying. Soon, it will be completely dead.

 

Probably has an iMac with an 8800 card. Those things are known to be defective, and will always die, not matter how many times replaced.