Is your dmg file not recognized by Mac system ? The Dmg files are used to install applications in the Mac system. The dmg files are first to be mounted in the Mac drive and then they can be installed. But if the dmg file not recognized then you can not install the application. You can check if the problem is with other dmg files or not by mounting them in the drive one by one. If they get mounted then the problem is with the that particular file and you can get a fresh copy of that. If none of the dmg files are mounting then the dmg file not recognized problem is with the Mac system itself. You can scan for the problem by using disk utility of Mac which can also try to fix it if possible. But in severe cases it may fail to fix dmg file not recognized problem so you have to format the drive. And after that you will be able mount the dmg file. Now for the data you have lost from the drive time machine can be used. When the time machine fails use the Mac data recovery software which can scan and recover your lost files. So when you have solved dmg file not recognized problem download the software and get back your files.