I have a 27" iMac, about a year old. Yesterday, when I read a "Verify Disk" on the HD, it told me that the startup disk needed to be repaired, requiring that I boot from my Snow Leopard install disk, but the computer won't book from the disk. It just stops on a grey screen with an apple logo - no turning cog or other action. I have tried the following: 1. I tried another Snow Leopard install disk, to see if the first was faulty. The iMac still refuses to boot, so I doubt it's the optical disk itself. 2. I tried the 10.4 install disk that came with the iMac. Same problem. 3. I held down the "C" key throughout the bootup process. Same problem. 4. I held down the "Option" key throughout the bootup process. Same problem. 5. I went to Setup/Startup Disk and directed it to startup from the Snow Leopard install disk. Same problem. 6. I cleared the PRAM and the NVRAM. Same problem. If I hold the eject button down thought the boot process, the SL install disk ejects, and the computer starts up normally, and it runs fine (except running verify disk still tells me the startup disk needs to be repaired). When the computer is running, the optical drive reads disks (including the SL install disks) just fine - it just won't boot from an optical disk. One thing that occurs to me as I write this is that the iMac is set to start in 64 bit mode. That shouldn't matter - but I may set it to 32 and see if it helps. All updates to Snow Leopard have been installed. No non-factory ram is installed. Any other thoughts? Help!