Random horizontal lines and crashes after upgrade

[oneofthesedaves]

I just upgraded a Core Duo iMac to Snow Leopard. It worked great until the moment when I installed Snow Leopard. Now I have random horizontal lines, crashes, and hangs. At the Apple store they hooked it up and did diagnostics. All the hardware is operating properly according to Apple. I have reset PRAM, reinstalled the OS 3 times, erased the hard drive and did a clean install, repaired disk permissions, repaired hd. It will work pretty well in safe mode, so that tells me it is a hardware issue. Any suggestions? I'm losing my mind. And no, it is not covered under Apple Care. And no, I don't have a copy of Leopard.

 

[oneofthesedaves]

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Sorry, I meant to say that since it works in safe mode it is likely a software issue