Chosen Solution
Hi, I have an iMac, it starts perfectly in safe mode, and I’ve already tried re-installing Snow Leopard and didn’t fix it. It just won’t start in “normal” mode.
As you can see the photos above, it goes light blue and then gives like a weird rectangle shape. Not sure if it’s an easy fix, i’m not very Mac literate. It works fine in safe mode, and there’s no ghosting or anything on the screen. Which made me think its maybe a HDD issue, but not entirely sure!
I suspect your VRAM is bad here on the graphics card as you get a checkered pattern. Your symptom of being able to use single user also supports this as the graphics driver will use shared RAM mode. I think you have one of the models like this one: iMac 21.5" (Mid-2010) Please tell us your exact model so we can aim you to the needed parts and IFIXIT guide you’ll need to follow to fix your system. Update (08/14/2017) OK, here’s the IFIXIT guide you’ll need to follow: iMac Intel 20" EMC 2133 and 2210 Video Card Replacement. And here’s the replacement GPU card: ATI Radeon HD 2400 XT (128 MB) - Apple P/N 661-4673 or the ATI Radeon HD 2600 XT PRO (256 MB) - Apple P/N 661-4672 You’ll also want to give this a try if you can get it to install in Safe mode: iMac (early 2008) ATI Radeon HD Graphics Firmware Update 1.0.1 in any case once you get the replacement GPU card you’ll want to double check its firmware.
