iMac - white screen, question mark - trying reinstall of OS X

I hate to be the bearer of bad news, but you're likely looking at either a corrupt partition on your hard drive or a hard drive failure.

Try rebooting the machine. Turn it off. When you turn it back on, quickly press+hold the "Option" key on your keyboard. After a few moments, your mouse cursor should appear on screen. If it isn't already, insert your Restore DVD. After a few moments to several minutes, an icon representing your DVD will appear. It will have an circular arrow pointing up a the icon below it. Click it.

The system should then use the DVD to boot up the computer, usually taking anywhere from a couple of minutes to 5 minutes. When the language selection screen appears, select your preferred language and continue/next. When the install dialog box appears, look up to the menu bar for the menu item entitled "Utilities". From the dropdown that appears, select "Disk Utility". This may take several minutes.

When the application launches, look to the left side-bar. Do you see an icon representing the hard drive? It will be small and begin with the size of the drive followed by the manufacturer (ie - toshiba, western digital, etc).

If the drive appears, click it to select it. You will see a new box appear to the right with several buttons. The button you'll want to check out is: "Repair Disk". Click it and observe to see whether the system is capable of fixing the issue.

If the drive does not appear in the left side-bar, then I'm sorry to say -- it's likely the drive has failed.

Either way, I would keep your Genius Bar appointment. While data recovery is not a service offered by Apple, they are usually pretty helpful in pointing you to local and national providers who can assist you.

Hope that helps.

how much did it cost? if i may know. because i have the same problem.