I recall a similar issue I had and I merely replaced the RAM sticks. Also
maxed out the RAM while I was at it. Problem solved.

On Tue, Mar 27, 2018 at 6:11 PM, <[email protected]> wrote:

> Thanks for the idea. However, this one (a 24" also) will not boot into
> Safe mode.
> In fact, I cannot get even a startup chime unless I pull one of the RAM
> cards out. It doesn't matter whether the left one is in or the right one is
> in, if I only have one RAM card in, it will produce the startup chime.
> However, I still have a black screen.
>
> I did try to set up an appointment at an Apple store, but since it is 10
> years old, they would not look at it.
>
> A couple of questions:
>
>    - If it is the video card, does the RAM card thing make any sense?
>    - If the video card was going out, should the Apple Hardware Test have
>    told me that when I ran it last week?
>    - Is there any way to be certain that the problem is the video card?
>
> Thanks!
>
> On Tuesday, March 27, 2018 at 8:11:50 AM UTC-6, ValterV wrote:
>>
>> Il giorno 27/03/18 03:17, "[email protected]" ha scritto:
>>
>> > The machine worked fine for about a week, but today when I tried to
>> wake
>> > it, I got a black and white checked screen.
>> Bummer. That screen makes me think about a damaged video card.
>>
>> I had a similar issue with an Early 2008 24" iMac: red vertical stripes
>> appeared all over the screen (bad video card), and the iMac froze on
>> startup.
>>
>> When I tried to boot in Safe mode, though (hold Shift key during
>> startup),
>> it did boot up. So I thought the video drivers were conflicting with the
>> (now) bad video card, hence the freeze at boot.
>> I disabled all of the drivers, and the iMac would boot fine (although
>> screen
>> redraw was sometimes slow).
>>
>> You can try booting in Safe mode and, if working, you may try my
>> workaround.
>>
>> Here's what I did:
>> - Remove all AMD/ATI kexts in /System/Library/Extensions
>> (it depends on your video card maker and model; mine was ATI Radeon 2600)
>> - Terminal: Touch "System/Library/Extensions"
>> - Delete "System/Library/Caches/com.apple.kext.caches" (in Finder)
>> - Reboot
>>
>> I wrote more details here:
>> http://www.mac-forums.com/apple-desktops/341784-imac-vertical-lines-screen-f
>>
>> rezees-boot.html#post1762659
>> <http://www.mac-forums.com/apple-desktops/341784-imac-vertical-lines-screen-frezees-boot.html#post1762659>
>>
>>
>>
>> --
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