This video is a step by step guide to reinstalling OSX Mountain Lion on a Macbook Pro.
1. Step one is to insert the OSX DVD into the slot drive of the Macbook Pro.
2. Start the install.
3. Agree to the Apple terms and conditions.
4. Select the local disk you want to install the OSX too.
5. Enter in your password to start the install.
6. Click Restart.
7. The OSX will install and it will restart again.
OSX Mountain Lion can be downloaded from Itunes and can be installed from the download package.