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 Release Next Generation iMac 80% Thinner
At the keynote which Apple is holding right now Phil Schiller has just shown of the next generation iMac.
The new iMac is 5mm thin which makes it 80% thinner then the previous generation and also comes in two size both 21″; and 27″; which have screen resolutions of 1920 x 1080 (21″;) and 2560 x 1440 (27″;). The new iMac comes with a 720p HD facetime camera , dual microphones you can also choose between flash storage or a normal HDD. You can add up to 32GB which is double the capacity of the previous generation. The new iMac comes with the either a i5 or i7.
These will ship sometime next month with the base model starting at $1299