Screen has green and pink lines and "snow"?

"David, what Dan is trying to do, is to determine if it is your video card/circuit or your LCD. So the best and quickest way is by attaching an external monitor. Here is what Apple says about your symptoms:""

Quick Check

Symptoms Quick Check

Vertical/Horizontal Lines

• Vertical lines

• Horizontal lines

1. Boot from install DVD to determine if potential software issue exists.

2. Verify if issue is visible on an external display.

Deep Dive

1. Boot from Install DVD and verify if issue is still visible:

• Flickering image

• Horizontal bands of static intermittently appear

• Dock and / or menu bar shift positions

• Display intermittently flashes on / off

Yes--> Go to Flickering issue, go to Noise / Unstable Flickering.

No--> Issue likely caused by software or driver issue. Troubleshoot for software

issues. Make sure all software updates have been installed.

2. Verify if issue is visible on an external display attached to mini DisplayPort.

Yes--> Issue NOT caused by internal LCD. For systems with a video card, go to step 3. For systems without a video card, go to step 4.

No--> Go to step 6.

3. If a video card is present, remove video card and inspect connector for damage or corrosion then reinstall. Verify if issue still occurs.

Yes--> Replace video card.

No--> Issue likely caused by poor video card connection.

4. For systems without video card,horizontal lines may be related to a failing RAM module. Verify if video issue only happens AFTER Apple logo and spinning wheel appear.

Yes--> Issue only happens AFTER Apple logo and spinning wheel appear. Go to step 5.

No--> Issue present before Apple logo and spinning wheel appear. Go to step 8.

5. Start with shift key down (safe mode) to disable system extensions. Verify if issue still

happens when booting in safe mode.

Yes--> Go to step 8.

No--> No video issue when booting in safe mode. Go to step 6.

6. Isolate with only one memory module installed, then with the other one. Test with knowngood

memory. Verify if issue only happens with specific RAM module(s).

Yes--> Replace affected RAM module.

No--> Go to step 7.

7. Isolate with one known-good memory module installed in one memory slot. Repeat by testing in other memory slots Verify if issue only happens with specific memory slot of logic board.

Yes--> Replace logic board and retest.

No--> Go to step 8.

8. Disconnect DisplayPort cable between LCD display and logic board, and verify if there is damage to cable or connectors.Repeat with vertical sync cable connected between LCD panel and LED backlight board.

Yes--> Replace DisplayPort cable and vertical sync cable or any other damaged part/module.

Go to step 9.

No--> Reinstall DisplayPort cable and vertical sync cable.

Go to step 9.

9. Verify if issue is still present after reinstalling internal DisplayPort cable and vertical sync cable.

Yes--> Replace logic board. If video card was present, reinstall original video card.

Go to step 10.

No--> Issue resolved.

10. Verify if issue is still present with replacement logic board installed.

Yes--> Go to step 11.

No--> Issue resolved.

11. Reinstall original logic board and verify if issue is still present with original logic board reinstalled.

Yes--> Replace LCD panel. Run Apple Service Display Utility.to verify the resolution of intermittent display flickering symptoms.

No--> Issue resolved. If a video card was present, reinstall original video card.""

So, I strongly advice that you follow Dan's way of doing things. Good luck."

"David - It sounds like either the display or GPU is failing. To help isolate out which can you connect an external monitor to your system. Does the display on it look OK? If it does then you know the display is having problems otherwise the GPU. Let us know what you find out.

As to the needed tools the iFixIt tool kit should meet your needs here Pro Tech Toolkit and a set of suction cups Heavy Duty Suction Cups and lastly, an ESD mat & wrist strap Anti Static Mat"

I had the same issue with my iMac 27 Mid 2010. Pink and green squares all over the screen. Threw my GPU in the oven 400f degrees for 9 mins. Problem solved.

"MY SOLUTION (working):

I was able to recover my iMac 27"" graphic card by open the computer and applying an electronic Contact Cleaner (I used M500 from BASTON.com.br), but there are many brands out there. I really didn't disconnected any inside cable, I just carefully pull up the display for at least to be able to see inside, since there are short and fragilely connected cables. I've followed ifix.com repair guide for this repair, but I didn't make all steps, again, I've just removed the eight T10 Torx screws securing the LCD to the outer case (to remove these screws I've used a standard screwdriver, without any trouble, despite the magnets attracting the tool and the screws. To put the screws back, I've needed to use two screwdrivers to position the screw correctly). Then, after shaking the product, I've applied the Contact Cleaner, from both sides, and from the top. Then, I left the computer alone for 20min. And finally, it has worked as it was new. Of course, ALL THIS SIMPLE PROCESS YOU NEED TO DO WITH THE ELECTRICITY CABEL DISCONNECTED. These cleaners are inflammable.

So, I didn't need to replace the graphic card, so I don't know if the cleaner has fixed some soldering connection, or if it was the dusty problem. Really, it has a lot of dusty inside, I have this iMac since 2009. But, really I din't cleaned it up properly, since I was afraid to disconnect the cables. I just applied the Cleaner, and it is working fine now. I reboot the imac again and again, and it boots perfectly now."