Install OS X replacing Windows on a Mac without losing data My brother installed Windows 7 on my Mac. Now I am trying to install OS X Lion  but when I select Reinstall OS X, I am not able to select any drive. One of my drive has 1.27 TB of data. Is it possible to install OS X without losing data?
There is no way to reinstall OS X without formatting and losing data. If you want to keep your data, recover the data to another drive or to the cloud.