Gray screen on boot

[cgalloway]

I am running Snowleopard on a 24" white imac bought in 2007. My system has been somewhat temperamental for a few weeks, crashing out on me when waking up and generating random artifacts onscreen during use. I noticed also that the hardrive recently renamed itself as "EMI Boot" when booting using the option key (although it worked fine).
Now, when booting, the apple logo appears, followed by the spinning wheel and a blank gray screen. Then nothing. The same thing happens when I try to boot using a mirrored backup drive or a separate bootable drive with a different version of OSX. The imac drive will, however, launch using a MBP in terminal mode without problem. I have run Diskwarrior and fsck on the drive. No difference. I've tested the RAM using memtest in single user mode. RAM seems OK. I dont have the original installation disks, so cannot run the diagnostics.
I'm coming to the conclusion that this may be a logic board problem but would appreciate any suggestions.

 

[Hellhammer]

Check out my guide!

 

[cgalloway]

Looking into this further, I get the feeling the problem is the graphics card, which in my case was the 661-4180 NVIDIA GeForce 7600 GT, available as a BTO. This card seems to have a high failure rate but is not integrated into the logic board and can be replaced seperately at places like:
http://www.welovemacs.com/6614180.html
Not exactly cheap, but better than the alternative
Is there any way, though, I can verify the problem is with my graphics card? The onscreen artifacts point to this, and while I do not pretend to understand the kernel panic reports generated by recent crashes, they generally contained references to the nvidia card.
I've now found my installation disk, but have been unable to get the imac to boot from it. My techtool pro boot disk is also useless.

 

[Hellhammer]

Looking into this further, I get the feeling the problem is the graphics card, which in my case was the 661-4180 NVIDIA GeForce 7600 GT, available as a BTO. This card seems to have a high failure rate but is not integrated into the logic board and can be replaced seperately at places like:
http://www.welovemacs.com/6614180.html
Not exactly cheap, but better than the alternative
Is there any way, though, I can verify the problem is with my graphics card? The onscreen artifacts point to this, and while I do not pretend to understand the kernel panic reports generated by recent crashes, they generally contained references to the nvidia card.
I've now found my installation disk, but have been unable to get the imac to boot from it. My techtool pro boot disk is also useless.

Hold down option key while booting and see what options does it give. It's hard to say what it is because some symptoms are hard drive related and others are logic board and GPU related. You could try replacing the HD first and see if that helps but I think you need to replace the logic board as well to get it work