OS X Lion dmg no mountable file systems is really a big issue because as long as this error persist your won't be able to install any application or software on your Mac system. The applications for Mac are available as a disk image file in the dmg format which has to be mounted on the Mac drive before installation. If you are getting osx lion dmg no mountable file systems then the installation can't occur and you will not able to use that. The possible reason can be that the file you are trying to mount is corrupted so you need to get a fresh copy of the file from its publisher. If the file is okay then the case of corruption can be with the drive itself which does allow the file to mount and you are facing error osx lion dmg no mountable file systems. You need to fix the corruption of the drive by using the disk utility and if it fails then format the drive. The lost data can be recovered from time machine backup or Mac data recovery software to make the complete recovery. You can use the software to scan the drive and then from the preview you will be able to select the files you want to recover. The software allows easy recovery for all types of files, so you should download the software and give it a try.