Hi, every time I turn on my IMAC, a file with a question mark appears and then the apple logo appears as well. I then get the timer thing to show its thinking and thats it.It just sticks on that! Any ideas how I can fix this?

U cannot start-up from your HD, please insert the installation CD into your computer and boot from the CD.

That's not very helpful dlink444. What the flashing question mark means is that your BIOS or BIOS equivalent cannot find a startup directory to run the OS from. Either it got deleted or corrupted but we deal with the problem the same in either case. You will need your OS disks. Place the first one in the drive and restart the computer. When you hear the boot tone, hold the 'C' key down to start from the disk rather than the hard drive. Progress through the screens until you see the Hard Drive to select the destination volume screen appear. There should be an "options" button in the lower left corner there. If you don't care about any of the data on the computer select the "clean install" option as this will erase the entire hard drive. If you do want to keep your data select the "archive and install" option while checking the "preserve user settings and accounts" button below that. This option will install just the OS while leaving your users folder intact. Proceed from there! Good luck!