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 Update OS X Mountain Lion Developer Preview 4 –
Apple released OS X Mountain Lion Preview 4 to developers last monday ahead of its release next month.
You can download the update via software updates in the Mac App store. It is unclear what has been fixed or added as they was not release notes but it is advised that all users update.
The update comes in at 1.08GB so do expect a very long download time
OS X Mountain Lion