My kids opened up minecraft the other day, which they have been playing for ages, selected one of there many worlds, but were unable to build or otherwise manipulate their world. The same for all the worlds they have built. I have an iMac OSX 10.9.4 2.9 GHz Intel Core i5 16 GB 1600 MHz DDR3 NVIDIA GeForce GT 650M 512 MB. I also have Java version 7 update 67 of and I updated Minecraft to the latest version. Any ideas what may be going on? Be gentle I know very little about computers and even less about minecraft. Thanks.
Help-Unable to manipulate minecraft world