Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple To Start Selling New iMacs Today ?
Apple first showed us the amazing new iMacs at the iPad mini event back in September but they did not give us a specific date orders would start. We have heard from a hand full of stores in the UK that they are expecting the new iMacs to be delivered sometime today but the rest have not heard anything. This could be because it is a new product and Apple want to keep the secrecy.
Our source can also back up the recent reports that you will be able to order your iMacs online today but if not for some reason then defiantly by Friday of this week.