I have an early 2008 Mac pro, with a 2.8 ghz quad core, 2 gb ram and a GeForce 8800 (basically factory spec) The computer has three hard drives. HDD A has Lion installed, HDD B has two partitions, Snow Leopard and Vista (don't laugh). HDD C is a time machine backup. I have been running with this configuration since Lion was released. Yesterday my computer froze, no spinning ball, but everything was non responsive. Strangely, I'm pretty sure that I could move the mouse. However I couldn't click on anything. Now when I try to boot up I get to the gray screen with the apple logo then the gear stops turning and the computer reboots. This is true for all of the partitions as well as the Lion recovery mode and booting from install disks (both the original disk and the Snow Leopard disk) and Mac safe mode. The only exception is that I have been able to successfully boot into Vista safe mode, but that isn't very useful to me. I have tried resetting the SMC and PRAM. Apple Hardware Test doesn't see any problems. I hadn't noticed any other problems leading up to this other than the fact that my RAM was never fully utilized, always about half a gig was sitting unused, even when I was editing massive files in photoshop. I don't think that this is a problem with the hard drives as I don't think that they would have both gone on the fritz at once and I am able to boot up Vista into safe mode. So... Is this the video card? The memory? Something else? Any advice would be greatly appreciated!