From Apple support, installs 10.9.2 latest version saves your stuff.
OS X Mavericks: Reinstall OS X
Use the built-in recovery disk to reinstall OS X while keeping your files and user settings intact.
Important: You must be connected to the Internet to reinstall OS X.
OS X Mavericks: Reinstall OS X
Use the built-in recovery disk to reinstall OS X while keeping your files and user settings intact.
Important: You must be connected to the Internet to reinstall OS X.
- Choose Apple menu > Restart. Once your Mac restarts (and the gray screen appears), hold down the Command (?) and R keys.
- If you're not connected to the Internet, choose a network from the Wi-Fi menu (in the top-right corner of the screen).
- Select Reinstall OS X, then click Continue.
- Follow the onscreen instructions. In the pane where you select a disk, select your current OS X disk (in most cases, it's the only one available).
