Hello, I was hoping someone might be able to help me narrow this problem down. My 3.06GHz 4GB 24" 2008 iMac w/ Nvidia 8800GS has stopped booting normally. This issue started gradually. Over the course of about a month, I'd have maybe a 50% chance making it through the boot process with the ability to use my computer, but the other 50% of times, I couldn't get past the login screen, at which point, the screen became filled with graphical artifacts, and stopped refreshing. This now happens 100% of the time, and will restart itself many of the times, endlessly. I tried each stick of ram, one at a time, tried booting OS X installed on a flash drive, resetting PRAM, all with no luck, and passed the Apple Hardware Test with flying colors. I'm inclined to think its a video card issue, but when booting from the install disk, and running disk utility, or the Apple Hardware Test, the problem doesn't occur at all. Is it possible that these modes do not use the Nvidia card? To reiterate, the graphical issue occurs immediately upon seeing the login screen (Mountain Lion). I replaced the (dead) hard drive with an SSD about 6 months ago, though, it appears to be working just fine, so I don't think that is the issue. Thanks for any help or suggestions!