iMac Video? problem, won't boot

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I have an iMac 24" 2.8ghz that won't boot up. The DVD drive and hard drive are tested to work, and I can get to the boot menu and select either to boot from. However after choosing either option the computer hangs and often displays a blank screen with only the mouse moving or a white screen with grey dots (like the apple logo exploded horizontally across the screen). I took a pic for reference DSCF6319.JPG .
Has anyone seen this before? Could this be a video card failure, or something else?
 

chscag

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2017 27" iMac, 10.5" iPad Pro, iPhone 8, iPhone 11, iPhone 12 Mini, Numerous iPods, Monterey
What happens when you attach an external monitor or TV to the iMac? Normal, or the same?
 
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RE: external video

I have to go out and get a mini dvi adapter. Will let you know if that works.
If an external works but not the main display is that the video card failing?
BTW, I tried booting a Linux disc and I heard sound with black screen.
 

chscag

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If an external works but not the main display is that the video card failing?

No. It means the main display has a problem. If both the iMac and external monitor show the same symptom, then it's likely a bad graphics chipset.
 
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When I hold the option key when I boot up it will show the hard drive and dvd drive just fine.
Just anything past that gets funky.
Thanks for your help!
 

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