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You are the third person in two days that reports a problem with a brand-new Late 2012 27-inch iMac.
The screen problem can't be repaired yourself. As you have a new iMac, the best thing you can do is to return it to Amazon and get a new one, or you can take it to an Apple Store and see if they can replace it at the moment you take it in. This is the only solution, as the display is damaged and replacing it yourself voids warranty
The Apple warranty is one year, irrespective of where you purchased the product. Try taking it to an Apple store genius bar and have it inspected for repair...Apple policy has been that computers will be repaired and not replaced. If a repair is not successful on the third attempt, then the computer may be replaced.
However, if you want a replacement your best bet is to deal with Amazon since they sold it and do not repair themselves.